diff --git a/.github/workflows/samples-kotlin-client.yaml b/.github/workflows/samples-kotlin-client.yaml
index 206cdbc0753e..3c86d9753afc 100644
--- a/.github/workflows/samples-kotlin-client.yaml
+++ b/.github/workflows/samples-kotlin-client.yaml
@@ -53,6 +53,8 @@ jobs:
           - samples/client/petstore/kotlin-enum-integers-multiplatform
           - samples/client/petstore/kotlin-array-simple-string-jvm-okhttp4
           - samples/client/petstore/kotlin-array-simple-string-multiplatform
+          - samples/client/petstore/kotlin-array-nullable-items
+          - samples/client/petstore/kotlin-array-nullable-items-multiplatform
           - samples/client/petstore/kotlin-bigdecimal-default-multiplatform
           - samples/client/petstore/kotlin-bigdecimal-default-okhttp4
           - samples/client/petstore/kotlin-jvm-jackson
diff --git a/bin/configs/kotlin-array-nullable-items-multiplatform.yaml b/bin/configs/kotlin-array-nullable-items-multiplatform.yaml
new file mode 100644
index 000000000000..341108d1d704
--- /dev/null
+++ b/bin/configs/kotlin-array-nullable-items-multiplatform.yaml
@@ -0,0 +1,8 @@
+generatorName: kotlin
+outputDir: samples/client/petstore/kotlin-array-nullable-items-multiplatform
+inputSpec: modules/openapi-generator/src/test/resources/3_0/kotlin/kotlin-array-nullable-items.yaml
+templateDir: modules/openapi-generator/src/main/resources/kotlin-client
+additionalProperties:
+  artifactId: kotlin-array-nullable-items-multiplatform
+  library: multiplatform
+  dateLibrary: kotlinx-datetime
diff --git a/bin/configs/kotlin-array-nullable-items.yaml b/bin/configs/kotlin-array-nullable-items.yaml
new file mode 100644
index 000000000000..c75b95ea2e96
--- /dev/null
+++ b/bin/configs/kotlin-array-nullable-items.yaml
@@ -0,0 +1,6 @@
+generatorName: kotlin
+outputDir: samples/client/petstore/kotlin-array-nullable-items
+inputSpec: modules/openapi-generator/src/test/resources/3_0/kotlin/kotlin-array-nullable-items.yaml
+templateDir: modules/openapi-generator/src/main/resources/kotlin-client
+additionalProperties:
+  artifactId: kotlin-array-nullable-items
diff --git a/modules/openapi-generator/src/main/resources/kotlin-client/data_class_opt_var.mustache b/modules/openapi-generator/src/main/resources/kotlin-client/data_class_opt_var.mustache
index abaf53a3b30a..ab4c5662f84b 100644
--- a/modules/openapi-generator/src/main/resources/kotlin-client/data_class_opt_var.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/data_class_opt_var.mustache
@@ -21,4 +21,4 @@
     {{#deprecated}}
     @Deprecated(message = "This property is deprecated.")
     {{/deprecated}}
-    {{#multiplatform}}@SerialName(value = "{{{vendorExtensions.x-base-name-literal}}}") {{/multiplatform}}{{#isInherited}}override {{/isInherited}}{{>modelMutable}} {{{name}}}: {{#isArray}}{{#isList}}kotlin.collections.{{#modelMutable}}Mutable{{/modelMutable}}{{#uniqueItems}}Set{{/uniqueItems}}{{^uniqueItems}}List{{/uniqueItems}}{{/isList}}{{^isList}}kotlin.Array{{/isList}}<{{^items.isEnum}}{{^items.isPrimitiveType}}{{^items.isModel}}{{#kotlinx_serialization}}@Contextual {{/kotlinx_serialization}}{{/items.isModel}}{{/items.isPrimitiveType}}{{{items.dataType}}}{{/items.isEnum}}{{#items.isEnum}}{{classname}}.{{{nameInPascalCase}}}{{/items.isEnum}}>{{/isArray}}{{^isEnum}}{{^isArray}}{{{dataType}}}{{/isArray}}{{/isEnum}}{{#isEnum}}{{^isArray}}{{classname}}.{{{nameInPascalCase}}}{{/isArray}}{{/isEnum}}? = {{^defaultValue}}null{{/defaultValue}}{{#defaultValue}}{{^isNumber}}{{{defaultValue}}}{{/isNumber}}{{#isNumber}}{{^multiplatform}}{{{dataType}}}("{{{defaultValue}}}"){{/multiplatform}}{{#multiplatform}}({{{defaultValue}}}).toDouble(){{/multiplatform}}{{/isNumber}}{{/defaultValue}}
\ No newline at end of file
+    {{#multiplatform}}@SerialName(value = "{{{vendorExtensions.x-base-name-literal}}}") {{/multiplatform}}{{#isInherited}}override {{/isInherited}}{{>modelMutable}} {{{name}}}: {{#isArray}}{{#isList}}kotlin.collections.{{#modelMutable}}Mutable{{/modelMutable}}{{#uniqueItems}}Set{{/uniqueItems}}{{^uniqueItems}}List{{/uniqueItems}}{{/isList}}{{^isList}}kotlin.Array{{/isList}}<{{^items.isEnum}}{{^items.isPrimitiveType}}{{^items.isModel}}{{#kotlinx_serialization}}@Contextual {{/kotlinx_serialization}}{{/items.isModel}}{{/items.isPrimitiveType}}{{{items.dataType}}}{{/items.isEnum}}{{#items.isEnum}}{{classname}}.{{{nameInPascalCase}}}{{/items.isEnum}}{{#items.isNullable}}?{{/items.isNullable}}>{{/isArray}}{{^isEnum}}{{^isArray}}{{{dataType}}}{{/isArray}}{{/isEnum}}{{#isEnum}}{{^isArray}}{{classname}}.{{{nameInPascalCase}}}{{/isArray}}{{/isEnum}}? = {{^defaultValue}}null{{/defaultValue}}{{#defaultValue}}{{^isNumber}}{{{defaultValue}}}{{/isNumber}}{{#isNumber}}{{^multiplatform}}{{{dataType}}}("{{{defaultValue}}}"){{/multiplatform}}{{#multiplatform}}({{{defaultValue}}}).toDouble(){{/multiplatform}}{{/isNumber}}{{/defaultValue}}
\ No newline at end of file
diff --git a/modules/openapi-generator/src/main/resources/kotlin-client/data_class_req_var.mustache b/modules/openapi-generator/src/main/resources/kotlin-client/data_class_req_var.mustache
index 0d9ec6067c5a..ebb3444af1f1 100644
--- a/modules/openapi-generator/src/main/resources/kotlin-client/data_class_req_var.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/data_class_req_var.mustache
@@ -21,4 +21,4 @@
     {{#deprecated}}
     @Deprecated(message = "This property is deprecated.")
     {{/deprecated}}
-    {{#multiplatform}}@SerialName(value = "{{{vendorExtensions.x-base-name-literal}}}") @Required {{/multiplatform}}{{#isInherited}}override {{/isInherited}}{{>modelMutable}} {{{name}}}: {{#isArray}}{{#isList}}kotlin.collections.{{#modelMutable}}Mutable{{/modelMutable}}{{#uniqueItems}}Set{{/uniqueItems}}{{^uniqueItems}}List{{/uniqueItems}}{{/isList}}{{^isList}}kotlin.Array{{/isList}}<{{^items.isEnum}}{{^items.isPrimitiveType}}{{^items.isModel}}{{#kotlinx_serialization}}@Contextual {{/kotlinx_serialization}}{{/items.isModel}}{{/items.isPrimitiveType}}{{{items.dataType}}}{{/items.isEnum}}{{#items.isEnum}}{{classname}}.{{{nameInPascalCase}}}{{/items.isEnum}}>{{/isArray}}{{^isEnum}}{{^isArray}}{{{dataType}}}{{/isArray}}{{/isEnum}}{{#isEnum}}{{^isArray}}{{classname}}.{{{nameInPascalCase}}}{{/isArray}}{{/isEnum}}{{#isNullable}}?{{/isNullable}}{{#defaultValue}} = {{^isNumber}}{{{defaultValue}}}{{/isNumber}}{{#isNumber}}{{^multiplatform}}{{{dataType}}}("{{{defaultValue}}}"){{/multiplatform}}{{#multiplatform}}({{{defaultValue}}}).toDouble(){{/multiplatform}}{{/isNumber}}{{/defaultValue}}
\ No newline at end of file
+    {{#multiplatform}}@SerialName(value = "{{{vendorExtensions.x-base-name-literal}}}") @Required {{/multiplatform}}{{#isInherited}}override {{/isInherited}}{{>modelMutable}} {{{name}}}: {{#isArray}}{{#isList}}kotlin.collections.{{#modelMutable}}Mutable{{/modelMutable}}{{#uniqueItems}}Set{{/uniqueItems}}{{^uniqueItems}}List{{/uniqueItems}}{{/isList}}{{^isList}}kotlin.Array{{/isList}}<{{^items.isEnum}}{{^items.isPrimitiveType}}{{^items.isModel}}{{#kotlinx_serialization}}@Contextual {{/kotlinx_serialization}}{{/items.isModel}}{{/items.isPrimitiveType}}{{{items.dataType}}}{{/items.isEnum}}{{#items.isEnum}}{{classname}}.{{{nameInPascalCase}}}{{/items.isEnum}}{{#items.isNullable}}?{{/items.isNullable}}>{{/isArray}}{{^isEnum}}{{^isArray}}{{{dataType}}}{{/isArray}}{{/isEnum}}{{#isEnum}}{{^isArray}}{{classname}}.{{{nameInPascalCase}}}{{/isArray}}{{/isEnum}}{{#isNullable}}?{{/isNullable}}{{#defaultValue}} = {{^isNumber}}{{{defaultValue}}}{{/isNumber}}{{#isNumber}}{{^multiplatform}}{{{dataType}}}("{{{defaultValue}}}"){{/multiplatform}}{{#multiplatform}}({{{defaultValue}}}).toDouble(){{/multiplatform}}{{/isNumber}}{{/defaultValue}}
\ No newline at end of file
diff --git a/modules/openapi-generator/src/main/resources/kotlin-client/interface_opt_var.mustache b/modules/openapi-generator/src/main/resources/kotlin-client/interface_opt_var.mustache
index 8d1449fea9c8..ec99fea193f7 100644
--- a/modules/openapi-generator/src/main/resources/kotlin-client/interface_opt_var.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/interface_opt_var.mustache
@@ -15,4 +15,4 @@
     {{^isEnum}}{{^isArray}}{{^isPrimitiveType}}{{^isModel}}@Contextual {{/isModel}}{{/isPrimitiveType}}{{/isArray}}{{/isEnum}}@SerialName(value = "{{{vendorExtensions.x-base-name-literal}}}")
     {{/kotlinx_serialization}}
     {{/multiplatform}}
-    {{#multiplatform}}@SerialName(value = "{{{vendorExtensions.x-base-name-literal}}}") abstract {{/multiplatform}}{{#kotlinx_serialization}}abstract {{/kotlinx_serialization}}{{>modelMutable}} {{{name}}}: {{#isArray}}{{#isList}}kotlin.collections.{{#modelMutable}}Mutable{{/modelMutable}}{{#uniqueItems}}Set{{/uniqueItems}}{{^uniqueItems}}List{{/uniqueItems}}{{/isList}}{{^isList}}kotlin.Array{{/isList}}<{{^items.isEnum}}{{^items.isPrimitiveType}}{{^items.isModel}}{{#kotlinx_serialization}}@Contextual {{/kotlinx_serialization}}{{/items.isModel}}{{/items.isPrimitiveType}}{{{items.dataType}}}{{/items.isEnum}}{{#items.isEnum}}{{classname}}.{{{nameInPascalCase}}}{{/items.isEnum}}>{{/isArray}}{{^isEnum}}{{^isArray}}{{{dataType}}}{{/isArray}}{{/isEnum}}{{#isEnum}}{{^isArray}}{{classname}}.{{{nameInPascalCase}}}{{/isArray}}{{/isEnum}}?
\ No newline at end of file
+    {{#multiplatform}}@SerialName(value = "{{{vendorExtensions.x-base-name-literal}}}") abstract {{/multiplatform}}{{#kotlinx_serialization}}abstract {{/kotlinx_serialization}}{{>modelMutable}} {{{name}}}: {{#isArray}}{{#isList}}kotlin.collections.{{#modelMutable}}Mutable{{/modelMutable}}{{#uniqueItems}}Set{{/uniqueItems}}{{^uniqueItems}}List{{/uniqueItems}}{{/isList}}{{^isList}}kotlin.Array{{/isList}}<{{^items.isEnum}}{{^items.isPrimitiveType}}{{^items.isModel}}{{#kotlinx_serialization}}@Contextual {{/kotlinx_serialization}}{{/items.isModel}}{{/items.isPrimitiveType}}{{{items.dataType}}}{{/items.isEnum}}{{#items.isEnum}}{{classname}}.{{{nameInPascalCase}}}{{/items.isEnum}}{{#items.isNullable}}?{{/items.isNullable}}>{{/isArray}}{{^isEnum}}{{^isArray}}{{{dataType}}}{{/isArray}}{{/isEnum}}{{#isEnum}}{{^isArray}}{{classname}}.{{{nameInPascalCase}}}{{/isArray}}{{/isEnum}}?
\ No newline at end of file
diff --git a/modules/openapi-generator/src/main/resources/kotlin-client/interface_req_var.mustache b/modules/openapi-generator/src/main/resources/kotlin-client/interface_req_var.mustache
index d863cfea8ebb..df210ffa5954 100644
--- a/modules/openapi-generator/src/main/resources/kotlin-client/interface_req_var.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/interface_req_var.mustache
@@ -15,4 +15,4 @@
     {{^isEnum}}{{^isArray}}{{^isPrimitiveType}}{{^isModel}}@Contextual {{/isModel}}{{/isPrimitiveType}}{{/isArray}}{{/isEnum}}@SerialName(value = "{{{vendorExtensions.x-base-name-literal}}}")
     {{/kotlinx_serialization}}
     {{/multiplatform}}
-    {{#multiplatform}}@SerialName(value = "{{{vendorExtensions.x-base-name-literal}}}") @Required abstract {{/multiplatform}}{{#kotlinx_serialization}}abstract {{/kotlinx_serialization}}{{>modelMutable}} {{{name}}}: {{#isArray}}{{#isList}}kotlin.collections.{{#modelMutable}}Mutable{{/modelMutable}}{{#uniqueItems}}Set{{/uniqueItems}}{{^uniqueItems}}List{{/uniqueItems}}{{/isList}}{{^isList}}kotlin.Array{{/isList}}<{{^items.isEnum}}{{^items.isPrimitiveType}}{{^items.isModel}}{{#kotlinx_serialization}}@Contextual {{/kotlinx_serialization}}{{/items.isModel}}{{/items.isPrimitiveType}}{{{items.dataType}}}{{/items.isEnum}}{{#items.isEnum}}{{classname}}.{{{nameInPascalCase}}}{{/items.isEnum}}>{{/isArray}}{{^isEnum}}{{^isArray}}{{{dataType}}}{{/isArray}}{{/isEnum}}{{#isEnum}}{{^isArray}}{{classname}}.{{{nameInPascalCase}}}{{/isArray}}{{/isEnum}}{{#isNullable}}?{{/isNullable}}
\ No newline at end of file
+    {{#multiplatform}}@SerialName(value = "{{{vendorExtensions.x-base-name-literal}}}") @Required abstract {{/multiplatform}}{{#kotlinx_serialization}}abstract {{/kotlinx_serialization}}{{>modelMutable}} {{{name}}}: {{#isArray}}{{#isList}}kotlin.collections.{{#modelMutable}}Mutable{{/modelMutable}}{{#uniqueItems}}Set{{/uniqueItems}}{{^uniqueItems}}List{{/uniqueItems}}{{/isList}}{{^isList}}kotlin.Array{{/isList}}<{{^items.isEnum}}{{^items.isPrimitiveType}}{{^items.isModel}}{{#kotlinx_serialization}}@Contextual {{/kotlinx_serialization}}{{/items.isModel}}{{/items.isPrimitiveType}}{{{items.dataType}}}{{/items.isEnum}}{{#items.isEnum}}{{classname}}.{{{nameInPascalCase}}}{{/items.isEnum}}{{#items.isNullable}}?{{/items.isNullable}}>{{/isArray}}{{^isEnum}}{{^isArray}}{{{dataType}}}{{/isArray}}{{/isEnum}}{{#isEnum}}{{^isArray}}{{classname}}.{{{nameInPascalCase}}}{{/isArray}}{{/isEnum}}{{#isNullable}}?{{/isNullable}}
\ No newline at end of file
diff --git a/modules/openapi-generator/src/test/resources/3_0/kotlin/kotlin-array-nullable-items.yaml b/modules/openapi-generator/src/test/resources/3_0/kotlin/kotlin-array-nullable-items.yaml
new file mode 100644
index 000000000000..4e91c97fdc77
--- /dev/null
+++ b/modules/openapi-generator/src/test/resources/3_0/kotlin/kotlin-array-nullable-items.yaml
@@ -0,0 +1,33 @@
+openapi: 3.0.0
+info:
+  title: 'Kotlin client — nullable array items'
+  description: Regression spec for nullable items inside list/array properties.
+  version: latest
+paths:
+  '/':
+    get:
+      operationId: getModel
+      responses:
+        '200':
+          description: Success
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/ArrayWithNullableItemsModel'
+components:
+  schemas:
+    ArrayWithNullableItemsModel:
+      type: object
+      required:
+        - requiredItems
+      properties:
+        requiredItems:
+          type: array
+          items:
+            type: string
+            nullable: true
+        optionalItems:
+          type: array
+          items:
+            type: string
+            nullable: true
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/.openapi-generator-ignore b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/.openapi-generator-ignore
new file mode 100644
index 000000000000..7484ee590a38
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/.openapi-generator-ignore
@@ -0,0 +1,23 @@
+# OpenAPI Generator Ignore
+# Generated by openapi-generator https://github.com/openapitools/openapi-generator
+
+# Use this file to prevent files from being overwritten by the generator.
+# The patterns follow closely to .gitignore or .dockerignore.
+
+# As an example, the C# client generator defines ApiClient.cs.
+# You can make changes and tell OpenAPI Generator to ignore just this file by uncommenting the following line:
+#ApiClient.cs
+
+# You can match any string of characters against a directory, file or extension with a single asterisk (*):
+#foo/*/qux
+# The above matches foo/bar/qux and foo/baz/qux, but not foo/bar/baz/qux
+
+# You can recursively match patterns against a directory, file or extension with a double asterisk (**):
+#foo/**/qux
+# This matches foo/bar/qux, foo/baz/qux, and foo/bar/baz/qux
+
+# You can also negate patterns with an exclamation (!).
+# For example, you can ignore all files in a docs folder with the file extension .md:
+#docs/*.md
+# Then explicitly reverse the ignore rule for a single file:
+#!docs/README.md
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/.openapi-generator/FILES b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/.openapi-generator/FILES
new file mode 100644
index 000000000000..b2f0a9d83a8d
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/.openapi-generator/FILES
@@ -0,0 +1,24 @@
+README.md
+build.gradle.kts
+docs/ArrayWithNullableItemsModel.md
+docs/DefaultApi.md
+gradle/wrapper/gradle-wrapper.jar
+gradle/wrapper/gradle-wrapper.properties
+gradlew
+gradlew.bat
+settings.gradle.kts
+src/commonMain/kotlin/org/openapitools/client/apis/DefaultApi.kt
+src/commonMain/kotlin/org/openapitools/client/auth/ApiKeyAuth.kt
+src/commonMain/kotlin/org/openapitools/client/auth/Authentication.kt
+src/commonMain/kotlin/org/openapitools/client/auth/HttpBasicAuth.kt
+src/commonMain/kotlin/org/openapitools/client/auth/HttpBearerAuth.kt
+src/commonMain/kotlin/org/openapitools/client/auth/OAuth.kt
+src/commonMain/kotlin/org/openapitools/client/infrastructure/ApiAbstractions.kt
+src/commonMain/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
+src/commonMain/kotlin/org/openapitools/client/infrastructure/Base64ByteArray.kt
+src/commonMain/kotlin/org/openapitools/client/infrastructure/HttpResponse.kt
+src/commonMain/kotlin/org/openapitools/client/infrastructure/OctetByteArray.kt
+src/commonMain/kotlin/org/openapitools/client/infrastructure/PartConfig.kt
+src/commonMain/kotlin/org/openapitools/client/infrastructure/RequestConfig.kt
+src/commonMain/kotlin/org/openapitools/client/infrastructure/RequestMethod.kt
+src/commonMain/kotlin/org/openapitools/client/models/ArrayWithNullableItemsModel.kt
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/.openapi-generator/VERSION b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/.openapi-generator/VERSION
new file mode 100644
index 000000000000..ca7bf6e46889
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/.openapi-generator/VERSION
@@ -0,0 +1 @@
+7.23.0-SNAPSHOT
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/README.md b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/README.md
new file mode 100644
index 000000000000..28fab72186e7
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/README.md
@@ -0,0 +1,52 @@
+# org.openapitools.client - Kotlin client library for Kotlin client — nullable array items
+
+Regression spec for nullable items inside list/array properties.
+
+## Overview
+This API client was generated by the [OpenAPI Generator](https://openapi-generator.tech) project.  By using the [openapi-spec](https://github.com/OAI/OpenAPI-Specification) from a remote server, you can easily generate an API client.
+
+- API version: latest
+- Package version: 
+- Generator version: 7.23.0-SNAPSHOT
+- Build package: org.openapitools.codegen.languages.KotlinClientCodegen
+
+## Requires
+
+* Kotlin 2.2.20
+
+## Build
+
+```
+./gradlew check assemble
+```
+
+This runs all tests and packages the library.
+
+## Features/Implementation Notes
+
+* Supports JSON inputs/outputs, File inputs, and Form inputs.
+* Supports collection formats for query parameters: csv, tsv, ssv, pipes.
+* Some Kotlin and Java types are fully qualified to avoid conflicts with types defined in OpenAPI definitions.
+
+
+<a id="documentation-for-api-endpoints"></a>
+## Documentation for API Endpoints
+
+All URIs are relative to *http://localhost*
+
+| Class | Method | HTTP request | Description |
+| ------------ | ------------- | ------------- | ------------- |
+| *DefaultApi* | [**getModel**](docs/DefaultApi.md#getmodel) | **GET** / |  |
+
+
+<a id="documentation-for-models"></a>
+## Documentation for Models
+
+ - [org.openapitools.client.models.ArrayWithNullableItemsModel](docs/ArrayWithNullableItemsModel.md)
+
+
+<a id="documentation-for-authorization"></a>
+## Documentation for Authorization
+
+Endpoints do not require authorization.
+
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/build.gradle.kts b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/build.gradle.kts
new file mode 100644
index 000000000000..c545c8032baf
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/build.gradle.kts
@@ -0,0 +1,97 @@
+import org.jetbrains.kotlin.gradle.plugin.mpp.KotlinNativeTarget
+
+plugins {
+    kotlin("multiplatform") version "2.2.20" // kotlin_version
+    kotlin("plugin.serialization") version "2.2.20" // kotlin_version
+}
+
+group = "org.openapitools"
+version = "1.0.0"
+
+val kotlin_version = "2.2.20"
+val coroutines_version = "1.10.2"
+val serialization_version = "1.9.0"
+val ktor_version = "3.2.3"
+
+repositories {
+    mavenCentral()
+}
+
+kotlin {
+    jvm()
+    iosX64()
+    iosArm64()
+    iosSimulatorArm64()
+    js {
+        browser()
+        nodejs()
+    }
+
+    sourceSets {
+        commonMain {
+            dependencies {
+                implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:$coroutines_version")
+                implementation("org.jetbrains.kotlinx:kotlinx-serialization-core:$serialization_version")
+
+                api("io.ktor:ktor-client-core:$ktor_version")
+                api("io.ktor:ktor-client-serialization:$ktor_version")
+                api("io.ktor:ktor-client-content-negotiation:$ktor_version")
+                api("io.ktor:ktor-serialization-kotlinx-json:$ktor_version")
+
+                api("org.jetbrains.kotlinx:kotlinx-datetime:0.7.1")
+            }
+        }
+
+        commonTest {
+            dependencies {
+                implementation(kotlin("test"))
+                implementation("io.ktor:ktor-client-mock:$ktor_version")
+            }
+        }
+
+        jvmMain {
+            dependencies {
+                implementation(kotlin("stdlib-jdk7"))
+                implementation("io.ktor:ktor-client-cio-jvm:$ktor_version")
+            }
+        }
+
+        jvmTest {
+            dependencies {
+                implementation(kotlin("test-junit"))
+            }
+        }
+
+        iosMain {
+            dependencies {
+                api("io.ktor:ktor-client-ios:$ktor_version")
+            }
+        }
+
+        jsMain {
+            dependencies {
+                api("io.ktor:ktor-client-js:$ktor_version")
+            }
+        }
+
+        all {
+            languageSettings {
+                optIn("kotlin.time.ExperimentalTime")
+            }
+        }
+    }
+}
+
+tasks {
+    register<Exec>("iosTest") {
+        val device = project.findProperty("device")?.toString() ?: "iPhone 8"
+        dependsOn("linkDebugTestIosX64")
+        group = JavaBasePlugin.VERIFICATION_GROUP
+        description = "Execute unit tests on ${device} simulator"
+        val binary = kotlin.targets.getByName<KotlinNativeTarget>("iosX64").binaries.getTest("DEBUG")
+        commandLine("xcrun", "simctl", "spawn", device, binary.outputFile)
+    }
+    register("test") {
+        dependsOn("allTests")
+    }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/docs/ArrayWithNullableItemsModel.md b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/docs/ArrayWithNullableItemsModel.md
new file mode 100644
index 000000000000..b72190023de1
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/docs/ArrayWithNullableItemsModel.md
@@ -0,0 +1,11 @@
+
+# ArrayWithNullableItemsModel
+
+## Properties
+| Name | Type | Description | Notes |
+| ------------ | ------------- | ------------- | ------------- |
+| **requiredItems** | **kotlin.collections.List&lt;kotlin.String?&gt;** |  |  |
+| **optionalItems** | **kotlin.collections.List&lt;kotlin.String?&gt;** |  |  [optional] |
+
+
+
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/docs/DefaultApi.md b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/docs/DefaultApi.md
new file mode 100644
index 000000000000..b0698436ab42
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/docs/DefaultApi.md
@@ -0,0 +1,50 @@
+# DefaultApi
+
+All URIs are relative to *http://localhost*
+
+| Method | HTTP request | Description |
+| ------------- | ------------- | ------------- |
+| [**getModel**](DefaultApi.md#getModel) | **GET** / |  |
+
+
+<a id="getModel"></a>
+# **getModel**
+> ArrayWithNullableItemsModel getModel()
+
+
+
+### Example
+```kotlin
+// Import classes:
+//import org.openapitools.client.infrastructure.*
+//import org.openapitools.client.models.*
+
+val apiInstance = DefaultApi()
+try {
+    val result : ArrayWithNullableItemsModel = apiInstance.getModel()
+    println(result)
+} catch (e: ClientException) {
+    println("4xx response calling DefaultApi#getModel")
+    e.printStackTrace()
+} catch (e: ServerException) {
+    println("5xx response calling DefaultApi#getModel")
+    e.printStackTrace()
+}
+```
+
+### Parameters
+This endpoint does not need any parameter.
+
+### Return type
+
+[**ArrayWithNullableItemsModel**](ArrayWithNullableItemsModel.md)
+
+### Authorization
+
+No authorization required
+
+### HTTP request headers
+
+ - **Content-Type**: Not defined
+ - **Accept**: application/json
+
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/gradle/wrapper/gradle-wrapper.jar b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/gradle/wrapper/gradle-wrapper.jar
new file mode 100644
index 000000000000..2c3521197d7c
Binary files /dev/null and b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/gradle/wrapper/gradle-wrapper.jar differ
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/gradle/wrapper/gradle-wrapper.properties b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/gradle/wrapper/gradle-wrapper.properties
new file mode 100644
index 000000000000..7705927e949f
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/gradle/wrapper/gradle-wrapper.properties
@@ -0,0 +1,7 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.14.3-all.zip
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/gradlew b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/gradlew
new file mode 100644
index 000000000000..51eb8bb47109
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/gradlew
@@ -0,0 +1,252 @@
+#!/bin/sh
+
+#
+# Copyright © 2015-2021 the original authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+##############################################################################
+#
+#   Gradle start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh Gradle
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/HEAD/platforms/jvm/plugins-application/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+[ -h "$app_path" ]
+do
+ls=$( ls -ld "$app_path" )
+link=${ls#*' -> '}
+case $link in             #(
+/*)   app_path=$link ;; #(
+*)    app_path=$APP_HOME$link ;;
+esac
+done
+
+# This is normally unused
+# shellcheck disable=SC2034
+APP_BASE_NAME=${0##*/}
+# Discard cd standard output in case $CDPATH is set (https://github.com/gradle/gradle/issues/25036)
+APP_HOME=$( cd -P "${APP_HOME:-./}" > /dev/null && printf '%s
+' "$PWD" ) || exit
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+echo "$*"
+} >&2
+
+die () {
+echo
+echo "$*"
+echo
+exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+CYGWIN* )         cygwin=true  ;; #(
+Darwin* )         darwin=true  ;; #(
+MSYS* | MINGW* )  msys=true    ;; #(
+NONSTOP* )        nonstop=true ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+# IBM's JDK on AIX uses strange locations for the executables
+JAVACMD=$JAVA_HOME/jre/sh/java
+else
+JAVACMD=$JAVA_HOME/bin/java
+fi
+if [ ! -x "$JAVACMD" ] ; then
+die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+else
+JAVACMD=java
+if ! command -v java >/dev/null 2>&1
+then
+die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+case $MAX_FD in #(
+max*)
+# In POSIX sh, ulimit -H is undefined. That's why the result is checked to see if it worked.
+# shellcheck disable=SC2039,SC3045
+MAX_FD=$( ulimit -H -n ) ||
+warn "Could not query maximum file descriptor limit"
+esac
+case $MAX_FD in  #(
+'' | soft) :;; #(
+*)
+# In POSIX sh, ulimit -n is undefined. That's why the result is checked to see if it worked.
+# shellcheck disable=SC2039,SC3045
+ulimit -n "$MAX_FD" ||
+warn "Could not set maximum file descriptor limit to $MAX_FD"
+esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
+
+JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+# Now convert the arguments - kludge to limit ourselves to /bin/sh
+for arg do
+if
+case $arg in                                #(
+-*)   false ;;                            # don't mess with options #(
+/?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+[ -e "$t" ] ;;                      #(
+*)    false ;;
+esac
+then
+arg=$( cygpath --path --ignore --mixed "$arg" )
+fi
+# Roll the args list around exactly as many times as the number of
+# args, so each arg winds up back in the position where it started, but
+# possibly modified.
+#
+# NB: a `for` loop captures its iteration list before it begins, so
+# changing the positional parameters here affects neither the number of
+# iterations, nor the values presented in `arg`.
+shift                   # remove old arg
+set -- "$@" "$arg"      # push replacement arg
+done
+fi
+
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Collect all arguments for the java command:
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, JAVA_OPTS, and optsEnvironmentVar are not allowed to contain shell fragments,
+#     and any embedded shellness will be escaped.
+#   * For example: A user cannot expect ${Hostname} to be expanded, as it is an environment variable and will be
+#     treated as '${Hostname}' itself on the command line.
+
+set -- \
+"-Dorg.gradle.appname=$APP_BASE_NAME" \
+-classpath "$CLASSPATH" \
+org.gradle.wrapper.GradleWrapperMain \
+"$@"
+
+# Stop when "xargs" is not available.
+if ! command -v xargs >/dev/null 2>&1
+then
+die "xargs is not available"
+fi
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+xargs -n1 |
+sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+tr '\n' ' '
+)" '"$@"'
+
+exec "$JAVACMD" "$@"
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/gradlew.bat b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/gradlew.bat
new file mode 100644
index 000000000000..9d21a21834d5
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/gradlew.bat
@@ -0,0 +1,94 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+@rem SPDX-License-Identifier: Apache-2.0
+@rem
+
+@if "%DEBUG%"=="" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%"=="" set DIRNAME=.
+@rem This is normally unused
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if %ERRORLEVEL% equ 0 goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH. 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME% 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if %ERRORLEVEL% equ 0 goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+set EXIT_CODE=%ERRORLEVEL%
+if %EXIT_CODE% equ 0 set EXIT_CODE=1
+if not ""=="%GRADLE_EXIT_CONSOLE%" exit %EXIT_CODE%
+exit /b %EXIT_CODE%
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/settings.gradle.kts b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/settings.gradle.kts
new file mode 100644
index 000000000000..4e6e5356c112
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/settings.gradle.kts
@@ -0,0 +1 @@
+rootProject.name = "kotlin-array-nullable-items-multiplatform"
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/apis/DefaultApi.kt b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/apis/DefaultApi.kt
new file mode 100644
index 000000000000..35774f6acb67
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/apis/DefaultApi.kt
@@ -0,0 +1,89 @@
+/**
+ *
+ * Please note:
+ * This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+ * Do not edit this file manually.
+ *
+ */
+
+@file:Suppress(
+    "ArrayInDataClass",
+    "DuplicatedCode",
+    "EnumEntryName",
+    "RemoveRedundantQualifierName",
+    "RemoveRedundantCallsOfConversionMethods",
+    "REDUNDANT_CALL_OF_CONVERSION_METHOD",
+    "RedundantUnitReturnType",
+    "RemoveEmptyClassBody",
+    "UnnecessaryVariable",
+    "UnusedImport",
+    "UnnecessaryVariable",
+    "unused"
+)
+
+package org.openapitools.client.apis
+
+import org.openapitools.client.models.ArrayWithNullableItemsModel
+
+import org.openapitools.client.infrastructure.*
+import io.ktor.client.HttpClient
+import io.ktor.client.HttpClientConfig
+import io.ktor.client.request.forms.formData
+import io.ktor.client.engine.HttpClientEngine
+import kotlinx.serialization.json.Json
+import io.ktor.http.ParametersBuilder
+import io.ktor.http.Headers
+import io.ktor.http.HttpHeaders
+import io.ktor.http.ContentType
+import io.ktor.http.content.PartData
+import kotlinx.serialization.*
+import kotlinx.serialization.descriptors.*
+import kotlinx.serialization.encoding.*
+
+open class DefaultApi : ApiClient {
+
+    constructor(
+        baseUrl: String = ApiClient.BASE_URL,
+        httpClientEngine: HttpClientEngine? = null,
+        httpClientConfig: ((HttpClientConfig<*>) -> Unit)? = null,
+        jsonSerializer: Json = ApiClient.JSON_DEFAULT
+    ) : super(baseUrl = baseUrl, httpClientEngine = httpClientEngine, httpClientConfig = httpClientConfig, jsonBlock = jsonSerializer)
+
+    constructor(
+        baseUrl: String,
+        httpClient: HttpClient
+    ): super(baseUrl = baseUrl, httpClient = httpClient)
+
+    /**
+     * 
+     * 
+     * @return ArrayWithNullableItemsModel
+     */
+    @Suppress("UNCHECKED_CAST")
+    open suspend fun getModel(): HttpResponse<ArrayWithNullableItemsModel> {
+
+        val localVariableAuthNames = listOf<String>()
+
+        val localVariableBody = 
+            io.ktor.client.utils.EmptyContent
+
+        val localVariableQuery = mutableMapOf<String, List<String>>()
+        val localVariableHeaders = mutableMapOf<String, String>()
+
+        val localVariableConfig = RequestConfig<kotlin.Any?>(
+            RequestMethod.GET,
+            "/",
+            query = localVariableQuery,
+            headers = localVariableHeaders,
+            requiresAuthentication = false,
+        )
+
+        return request(
+            localVariableConfig,
+            localVariableBody,
+            localVariableAuthNames
+        ).wrap()
+    }
+
+
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/auth/ApiKeyAuth.kt b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/auth/ApiKeyAuth.kt
new file mode 100644
index 000000000000..8bd8b59a8f82
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/auth/ApiKeyAuth.kt
@@ -0,0 +1,16 @@
+package org.openapitools.client.auth
+
+class ApiKeyAuth(private val location: String, val paramName: String) : Authentication {
+    var apiKey: String? = null
+    var apiKeyPrefix: String? = null
+
+    override fun apply(query: MutableMap<String, List<String>>, headers: MutableMap<String, String>) {
+        val key: String = apiKey ?: return
+        val prefix: String? = apiKeyPrefix
+        val value: String = if (prefix != null) "$prefix $key" else key
+        when (location) {
+            "query" -> query[paramName] = listOf(value)
+            "header" -> headers[paramName] = value
+        }
+    }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/auth/Authentication.kt b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/auth/Authentication.kt
new file mode 100644
index 000000000000..2c5dfb4acc56
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/auth/Authentication.kt
@@ -0,0 +1,13 @@
+package org.openapitools.client.auth
+
+interface Authentication {
+
+    /**
+     * Apply authentication settings to header and query params.
+     *
+     * @param query Query parameters.
+     * @param headers Header parameters.
+     */
+    fun apply(query: MutableMap<String, List<String>>, headers: MutableMap<String, String>)
+
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/auth/HttpBasicAuth.kt b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/auth/HttpBasicAuth.kt
new file mode 100644
index 000000000000..b4aecdc99658
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/auth/HttpBasicAuth.kt
@@ -0,0 +1,15 @@
+package org.openapitools.client.auth
+
+import kotlin.io.encoding.Base64
+
+class HttpBasicAuth : Authentication {
+    var username: String? = null
+    var password: String? = null
+
+    override fun apply(query: MutableMap<String, List<String>>, headers: MutableMap<String, String>) {
+        if (username == null && password == null) return
+        val str = (username ?: "") + ":" + (password ?: "")
+        val auth = Base64.encode(str.encodeToByteArray())
+        headers["Authorization"] = "Basic $auth"
+    }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/auth/HttpBearerAuth.kt b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/auth/HttpBearerAuth.kt
new file mode 100644
index 000000000000..a6fb285af5c3
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/auth/HttpBearerAuth.kt
@@ -0,0 +1,14 @@
+package org.openapitools.client.auth
+
+class HttpBearerAuth(private val scheme: String?) : Authentication {
+    var bearerToken: String? = null
+
+    override fun apply(query: MutableMap<String, List<String>>, headers: MutableMap<String, String>) {
+        val token: String = bearerToken ?: return
+        headers["Authorization"] = (if (scheme != null) upperCaseBearer(scheme)!! + " " else "") + token
+    }
+
+    private fun upperCaseBearer(scheme: String): String? {
+        return if ("bearer".equals(scheme, ignoreCase = true)) "Bearer" else scheme
+    }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/auth/OAuth.kt b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/auth/OAuth.kt
new file mode 100644
index 000000000000..0e8f30f39383
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/auth/OAuth.kt
@@ -0,0 +1,10 @@
+package org.openapitools.client.auth
+
+class OAuth : Authentication {
+    var accessToken: String? = null
+
+    override fun apply(query: MutableMap<String, List<String>>, headers: MutableMap<String, String>) {
+        val token: String = accessToken ?: return
+        headers["Authorization"] = "Bearer $token"
+    }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/ApiAbstractions.kt b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/ApiAbstractions.kt
new file mode 100644
index 000000000000..7fe8da468374
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/ApiAbstractions.kt
@@ -0,0 +1,23 @@
+package org.openapitools.client.infrastructure
+
+typealias MultiValueMap = MutableMap<String,List<String>>
+
+fun collectionDelimiter(collectionFormat: String): String = when(collectionFormat) {
+    "csv" -> ","
+    "tsv" -> "\t"
+    "pipe" -> "|"
+    "space" -> " "
+    else -> ""
+}
+
+val defaultMultiValueConverter: (item: Any?) -> String = { item -> "$item" }
+
+fun <T : Any?> toMultiValue(items: Array<T>, collectionFormat: String, map: (item: T) -> String = defaultMultiValueConverter): List<String>
+        = toMultiValue(items.asIterable(), collectionFormat, map)
+
+fun <T : Any?> toMultiValue(items: Iterable<T>, collectionFormat: String, map: (item: T) -> String = defaultMultiValueConverter): List<String> {
+    return when(collectionFormat) {
+        "multi" -> items.map(map)
+        else -> listOf(items.joinToString(separator = collectionDelimiter(collectionFormat), transform = map))
+    }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/ApiClient.kt b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
new file mode 100644
index 000000000000..081b4b08c51f
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
@@ -0,0 +1,188 @@
+package org.openapitools.client.infrastructure
+
+import io.ktor.client.HttpClient
+import io.ktor.client.HttpClientConfig
+import io.ktor.client.engine.HttpClientEngine
+import io.ktor.client.plugins.contentnegotiation.ContentNegotiation
+import io.ktor.client.request.*
+import io.ktor.client.request.forms.FormDataContent
+import io.ktor.client.request.forms.MultiPartFormDataContent
+import io.ktor.client.request.header
+import io.ktor.client.request.parameter
+import io.ktor.client.statement.HttpResponse
+import io.ktor.http.ContentType
+import io.ktor.serialization.kotlinx.json.json
+import io.ktor.http.*
+import io.ktor.http.content.PartData
+import io.ktor.http.contentType
+import kotlin.Unit
+import kotlinx.serialization.json.Json
+
+import org.openapitools.client.auth.*
+
+open class ApiClient(
+        private val baseUrl: String
+) {
+
+    private lateinit var client: HttpClient
+
+    constructor(
+        baseUrl: String,
+        httpClientEngine: HttpClientEngine?,
+        httpClientConfig: ((HttpClientConfig<*>) -> Unit)? = null,
+        jsonBlock: Json,
+    ) : this(baseUrl = baseUrl) {
+        val clientConfig: (HttpClientConfig<*>) -> Unit by lazy {
+            {
+                it.install(ContentNegotiation) { json(jsonBlock) }
+                httpClientConfig?.invoke(it)
+            }
+        }
+
+        client = httpClientEngine?.let { HttpClient(it, clientConfig) } ?: HttpClient(clientConfig)
+    }
+
+    constructor(
+        baseUrl: String,
+        httpClient: HttpClient
+    ): this(baseUrl = baseUrl) {
+        this.client = httpClient
+    }
+
+    private val authentications: kotlin.collections.Map<String, Authentication>? = null
+
+    companion object {
+        const val BASE_URL: String = "http://localhost"
+        val JSON_DEFAULT: Json = Json {
+          ignoreUnknownKeys = true
+          prettyPrint = true
+          isLenient = true
+        }
+        protected val UNSAFE_HEADERS: List<String> = listOf(HttpHeaders.ContentType)
+    }
+
+    /**
+     * Set the username for the first HTTP basic authentication.
+     *
+     * @param username Username
+     */
+    fun setUsername(username: String) {
+        val auth = authentications?.values?.firstOrNull { it is HttpBasicAuth } as HttpBasicAuth?
+                ?: throw Exception("No HTTP basic authentication configured")
+        auth.username = username
+    }
+
+    /**
+     * Set the password for the first HTTP basic authentication.
+     *
+     * @param password Password
+     */
+    fun setPassword(password: String) {
+        val auth = authentications?.values?.firstOrNull { it is HttpBasicAuth } as HttpBasicAuth?
+                ?: throw Exception("No HTTP basic authentication configured")
+        auth.password = password
+    }
+
+    /**
+     * Set the API key value for the first API key authentication.
+     *
+     * @param apiKey API key
+     * @param paramName The name of the API key parameter, or null or set the first key.
+     */
+    fun setApiKey(apiKey: String, paramName: String? = null) {
+        val auth = authentications?.values?.firstOrNull { it is ApiKeyAuth && (paramName == null || paramName == it.paramName)} as ApiKeyAuth?
+                ?: throw Exception("No API key authentication configured")
+        auth.apiKey = apiKey
+    }
+
+    /**
+     * Set the API key prefix for the first API key authentication.
+     *
+     * @param apiKeyPrefix API key prefix
+     * @param paramName The name of the API key parameter, or null or set the first key.
+     */
+    fun setApiKeyPrefix(apiKeyPrefix: String, paramName: String? = null) {
+        val auth = authentications?.values?.firstOrNull { it is ApiKeyAuth && (paramName == null || paramName == it.paramName) } as ApiKeyAuth?
+                ?: throw Exception("No API key authentication configured")
+        auth.apiKeyPrefix = apiKeyPrefix
+    }
+
+    /**
+     * Set the access token for the first OAuth2 authentication.
+     *
+     * @param accessToken Access token
+     */
+    fun setAccessToken(accessToken: String) {
+        val auth = authentications?.values?.firstOrNull { it is OAuth } as OAuth?
+                ?: throw Exception("No OAuth2 authentication configured")
+        auth.accessToken = accessToken
+    }
+
+    /**
+     * Set the access token for the first Bearer authentication.
+     *
+     * @param bearerToken The bearer token.
+     */
+    fun setBearerToken(bearerToken: String) {
+        val auth = authentications?.values?.firstOrNull { it is HttpBearerAuth } as HttpBearerAuth?
+                ?: throw Exception("No Bearer authentication configured")
+        auth.bearerToken = bearerToken
+    }
+
+    protected suspend fun <T: Any?> multipartFormRequest(requestConfig: RequestConfig<T>, body: kotlin.collections.List<PartData>?, authNames: kotlin.collections.List<String>): HttpResponse {
+        return request(requestConfig, MultiPartFormDataContent(body ?: listOf()), authNames)
+    }
+
+    protected suspend fun <T: Any?> urlEncodedFormRequest(requestConfig: RequestConfig<T>, body: Parameters?, authNames: kotlin.collections.List<String>): HttpResponse {
+        return request(requestConfig, FormDataContent(body ?: Parameters.Empty), authNames)
+    }
+
+    protected suspend fun <T: Any?> jsonRequest(requestConfig: RequestConfig<T>, body: Any? = null, authNames: kotlin.collections.List<String>): HttpResponse = request(requestConfig, body, authNames)
+
+    protected suspend fun <T: Any?> request(requestConfig: RequestConfig<T>, body: Any? = null, authNames: kotlin.collections.List<String>): HttpResponse {
+        requestConfig.updateForAuth<T>(authNames)
+        val headers = requestConfig.headers
+
+        return client.request {
+            this.url {
+                this.takeFrom(URLBuilder(baseUrl))
+                appendPath(requestConfig.path.trimStart('/').split('/'))
+                requestConfig.query.forEach { query ->
+                    query.value.forEach { value ->
+                        parameter(query.key, value)
+                    }
+                }
+            }
+            this.method = requestConfig.method.httpMethod
+            headers.filter { header -> !UNSAFE_HEADERS.contains(header.key) }.forEach { header -> this.header(header.key, header.value) }
+            if (requestConfig.method in listOf(RequestMethod.PUT, RequestMethod.POST, RequestMethod.PATCH)) {
+                val contentType = (requestConfig.headers[HttpHeaders.ContentType]?.let { ContentType.parse(it) }
+                    ?: ContentType.Application.Json)
+                this.contentType(contentType)
+                this.setBody(body)
+            }
+        }
+    }
+
+    private fun <T: Any?> RequestConfig<T>.updateForAuth(authNames: kotlin.collections.List<String>) {
+        for (authName in authNames) {
+            val auth = authentications?.get(authName) ?: throw Exception("Authentication undefined: $authName")
+            auth.apply(query, headers)
+        }
+    }
+
+    private fun URLBuilder.appendPath(components: kotlin.collections.List<String>): URLBuilder = apply {
+        encodedPath = encodedPath.trimEnd('/') + components.joinToString("/", prefix = "/") { it.encodeURLQueryComponent() }
+    }
+
+    private val RequestMethod.httpMethod: HttpMethod
+        get() = when (this) {
+            RequestMethod.DELETE -> HttpMethod.Delete
+            RequestMethod.GET -> HttpMethod.Get
+            RequestMethod.HEAD -> HttpMethod.Head
+            RequestMethod.PATCH -> HttpMethod.Patch
+            RequestMethod.PUT -> HttpMethod.Put
+            RequestMethod.POST -> HttpMethod.Post
+            RequestMethod.OPTIONS -> HttpMethod.Options
+        }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/Base64ByteArray.kt b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/Base64ByteArray.kt
new file mode 100644
index 000000000000..0fda8e759f0c
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/Base64ByteArray.kt
@@ -0,0 +1,30 @@
+package org.openapitools.client.infrastructure
+
+import kotlinx.serialization.*
+import kotlinx.serialization.descriptors.*
+import kotlinx.serialization.encoding.*
+import kotlin.io.encoding.Base64
+
+@Serializable(Base64ByteArray.Companion::class)
+class Base64ByteArray(val value: ByteArray) {
+    companion object : KSerializer<Base64ByteArray> {
+        override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("Base64ByteArray", PrimitiveKind.STRING)
+        override fun serialize(encoder: Encoder, value: Base64ByteArray): Unit = encoder.encodeString(Base64.encode(value.value))
+        override fun deserialize(decoder: Decoder): Base64ByteArray = Base64ByteArray(Base64.decode(decoder.decodeString()))
+    }
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (other == null || this::class != other::class) return false
+        other as Base64ByteArray
+        return value.contentEquals(other.value)
+    }
+
+    override fun hashCode(): Int {
+        return value.contentHashCode()
+    }
+
+    override fun toString(): String {
+        return "Base64ByteArray(${value.toHexString()})"
+    }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/HttpResponse.kt b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/HttpResponse.kt
new file mode 100644
index 000000000000..4285d605ea62
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/HttpResponse.kt
@@ -0,0 +1,51 @@
+package org.openapitools.client.infrastructure
+
+import io.ktor.http.Headers
+import io.ktor.http.isSuccess
+import io.ktor.util.reflect.TypeInfo
+import io.ktor.util.reflect.typeInfo
+
+open class HttpResponse<T : Any>(val response: io.ktor.client.statement.HttpResponse, val provider: BodyProvider<T>) {
+    val status: Int = response.status.value
+    val success: Boolean = response.status.isSuccess()
+    val headers: Map<String, List<String>> = response.headers.mapEntries()
+    suspend fun body(): T = provider.body(response)
+    suspend fun <V : Any> typedBody(type: TypeInfo): V = provider.typedBody(response, type)
+
+    companion object {
+        private fun Headers.mapEntries(): Map<String, List<String>> {
+            val result = mutableMapOf<String, List<String>>()
+            entries().forEach { result[it.key] = it.value }
+            return result
+        }
+    }
+}
+
+interface BodyProvider<T : Any> {
+    suspend fun body(response: io.ktor.client.statement.HttpResponse): T
+    suspend fun <V : Any> typedBody(response: io.ktor.client.statement.HttpResponse, type: TypeInfo): V
+}
+
+class TypedBodyProvider<T : Any>(private val type: TypeInfo) : BodyProvider<T> {
+    @Suppress("UNCHECKED_CAST")
+    override suspend fun body(response: io.ktor.client.statement.HttpResponse): T =
+            response.call.body(type) as T
+
+    @Suppress("UNCHECKED_CAST")
+    override suspend fun <V : Any> typedBody(response: io.ktor.client.statement.HttpResponse, type: TypeInfo): V =
+            response.call.body(type) as V
+}
+
+class MappedBodyProvider<S : Any, T : Any>(private val provider: BodyProvider<S>, private val block: S.() -> T) : BodyProvider<T> {
+    override suspend fun body(response: io.ktor.client.statement.HttpResponse): T =
+            block(provider.body(response))
+
+    override suspend fun <V : Any> typedBody(response: io.ktor.client.statement.HttpResponse, type: TypeInfo): V =
+            provider.typedBody(response, type)
+}
+
+inline fun <reified T : Any> io.ktor.client.statement.HttpResponse.wrap(): HttpResponse<T> =
+        HttpResponse(this, TypedBodyProvider(typeInfo<T>()))
+
+fun <T : Any, V : Any> HttpResponse<T>.map(block: T.() -> V): HttpResponse<V> =
+        HttpResponse(response, MappedBodyProvider(provider, block))
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/OctetByteArray.kt b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/OctetByteArray.kt
new file mode 100644
index 000000000000..5c4b29cd595f
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/OctetByteArray.kt
@@ -0,0 +1,29 @@
+package org.openapitools.client.infrastructure
+
+import kotlinx.serialization.*
+import kotlinx.serialization.descriptors.*
+import kotlinx.serialization.encoding.*
+
+@Serializable(OctetByteArray.Companion::class)
+class OctetByteArray(val value: ByteArray) {
+    companion object : KSerializer<OctetByteArray> {
+        override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("OctetByteArray", PrimitiveKind.STRING)
+        override fun serialize(encoder: Encoder, value: OctetByteArray): Unit = encoder.encodeString(value.value.toHexString())
+        override fun deserialize(decoder: Decoder): OctetByteArray = OctetByteArray(decoder.decodeString().hexToByteArray())
+    }
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (other == null || this::class != other::class) return false
+        other as OctetByteArray
+        return value.contentEquals(other.value)
+    }
+
+    override fun hashCode(): Int {
+        return value.contentHashCode()
+    }
+
+    override fun toString(): String {
+        return "OctetByteArray(${value.toHexString()})"
+    }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/PartConfig.kt b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/PartConfig.kt
new file mode 100644
index 000000000000..c2a5c99ec7e6
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/PartConfig.kt
@@ -0,0 +1,19 @@
+package org.openapitools.client.infrastructure
+
+/**
+ * Defines a config object for a given part of a multi-part request.
+ * NOTE: Headers is a Map<String,String> because rfc2616 defines
+ *       multi-valued headers as csv-only.
+ * 
+ * @property headers The headers for this part
+ * @property body The body content for this part
+ * @property serializer Optional custom serializer for JSON content. When provided, this will be
+ *                      used instead of the default serialization for parts with application/json
+ *                      content-type. This allows capturing type information at the call site to
+ *                      avoid issues with type erasure in kotlinx.serialization.
+ */
+data class PartConfig<T>(
+    val headers: MutableMap<String, String> = mutableMapOf(),
+    val body: T? = null,
+    val serializer: ((Any?) -> String)? = null
+)
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/RequestConfig.kt b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/RequestConfig.kt
new file mode 100644
index 000000000000..6578b9381b78
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/RequestConfig.kt
@@ -0,0 +1,19 @@
+package org.openapitools.client.infrastructure
+
+/**
+ * Defines a config object for a given request.
+ * NOTE: This object doesn't include 'body' because it
+ *       allows for caching of the constructed object
+ *       for many request definitions.
+ * NOTE: Headers is a Map<String,String> because rfc2616 defines
+ *       multi-valued headers as csv-only.
+ */
+data class RequestConfig<T>(
+    val method: RequestMethod,
+    val path: String,
+    val headers: MutableMap<String, String> = mutableMapOf(),
+    val params: MutableMap<String, Any> = mutableMapOf(),
+    val query: MutableMap<String, List<String>> = mutableMapOf(),
+    val requiresAuthentication: Boolean,
+    val body: T? = null
+)
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/RequestMethod.kt b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/RequestMethod.kt
new file mode 100644
index 000000000000..beb56f07cdde
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/infrastructure/RequestMethod.kt
@@ -0,0 +1,8 @@
+package org.openapitools.client.infrastructure
+
+/**
+ * Provides enumerated HTTP verbs
+ */
+enum class RequestMethod {
+    GET, DELETE, HEAD, OPTIONS, PATCH, POST, PUT
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/models/ArrayWithNullableItemsModel.kt b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/models/ArrayWithNullableItemsModel.kt
new file mode 100644
index 000000000000..f4d39b12519b
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/commonMain/kotlin/org/openapitools/client/models/ArrayWithNullableItemsModel.kt
@@ -0,0 +1,49 @@
+/**
+ *
+ * Please note:
+ * This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+ * Do not edit this file manually.
+ *
+ */
+
+@file:Suppress(
+    "ArrayInDataClass",
+    "DuplicatedCode",
+    "EnumEntryName",
+    "RemoveRedundantQualifierName",
+    "RemoveRedundantCallsOfConversionMethods",
+    "REDUNDANT_CALL_OF_CONVERSION_METHOD",
+    "RedundantUnitReturnType",
+    "RemoveEmptyClassBody",
+    "UnnecessaryVariable",
+    "UnusedImport",
+    "UnnecessaryVariable",
+    "unused"
+)
+
+package org.openapitools.client.models
+
+
+import kotlinx.serialization.*
+import kotlinx.serialization.descriptors.*
+import kotlinx.serialization.encoding.*
+
+/**
+ * 
+ *
+ * @param requiredItems 
+ * @param optionalItems 
+ */
+@Serializable
+
+data class ArrayWithNullableItemsModel (
+
+    @SerialName(value = "requiredItems") @Required val requiredItems: kotlin.collections.List<kotlin.String?>,
+
+    @SerialName(value = "optionalItems") val optionalItems: kotlin.collections.List<kotlin.String?>? = null
+
+) {
+
+
+}
+
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/test/kotlin/org/openapitools/client/apis/DefaultApiTest.kt b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/test/kotlin/org/openapitools/client/apis/DefaultApiTest.kt
new file mode 100644
index 000000000000..d2700e179dd5
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/test/kotlin/org/openapitools/client/apis/DefaultApiTest.kt
@@ -0,0 +1,45 @@
+/**
+ *
+ * Please note:
+ * This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+ * Do not edit this file manually.
+ *
+ */
+
+@file:Suppress(
+    "ArrayInDataClass",
+    "DuplicatedCode",
+    "EnumEntryName",
+    "RemoveRedundantQualifierName",
+    "RemoveRedundantCallsOfConversionMethods",
+    "REDUNDANT_CALL_OF_CONVERSION_METHOD",
+    "RedundantUnitReturnType",
+    "RemoveEmptyClassBody",
+    "UnnecessaryVariable",
+    "UnusedImport",
+    "UnnecessaryVariable",
+    "unused"
+)
+
+package org.openapitools.client.apis
+
+import io.kotlintest.shouldBe
+import io.kotlintest.specs.ShouldSpec
+
+import org.openapitools.client.apis.DefaultApi
+import org.openapitools.client.models.ArrayWithNullableItemsModel
+
+class DefaultApiTest : ShouldSpec() {
+    init {
+        // uncomment below to create an instance of DefaultApi
+        //val apiInstance = DefaultApi()
+
+        // to test getModel
+        should("test getModel") {
+            // uncomment below to test getModel
+            //val result : ArrayWithNullableItemsModel = apiInstance.getModel()
+            //result shouldBe ("TODO")
+        }
+
+    }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/test/kotlin/org/openapitools/client/models/ArrayWithNullableItemsModelTest.kt b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/test/kotlin/org/openapitools/client/models/ArrayWithNullableItemsModelTest.kt
new file mode 100644
index 000000000000..c99c9d5e8b92
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items-multiplatform/src/test/kotlin/org/openapitools/client/models/ArrayWithNullableItemsModelTest.kt
@@ -0,0 +1,49 @@
+/**
+ *
+ * Please note:
+ * This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+ * Do not edit this file manually.
+ *
+ */
+
+@file:Suppress(
+    "ArrayInDataClass",
+    "DuplicatedCode",
+    "EnumEntryName",
+    "RemoveRedundantQualifierName",
+    "RemoveRedundantCallsOfConversionMethods",
+    "REDUNDANT_CALL_OF_CONVERSION_METHOD",
+    "RedundantUnitReturnType",
+    "RemoveEmptyClassBody",
+    "UnnecessaryVariable",
+    "UnusedImport",
+    "UnnecessaryVariable",
+    "unused"
+)
+
+package org.openapitools.client.models
+
+import io.kotlintest.shouldBe
+import io.kotlintest.specs.ShouldSpec
+
+import org.openapitools.client.models.ArrayWithNullableItemsModel
+
+class ArrayWithNullableItemsModelTest : ShouldSpec() {
+    init {
+        // uncomment below to create an instance of ArrayWithNullableItemsModel
+        //val modelInstance = ArrayWithNullableItemsModel()
+
+        // to test the property `requiredItems`
+        should("test requiredItems") {
+            // uncomment below to test the property
+            //modelInstance.requiredItems shouldBe ("TODO")
+        }
+
+        // to test the property `optionalItems`
+        should("test optionalItems") {
+            // uncomment below to test the property
+            //modelInstance.optionalItems shouldBe ("TODO")
+        }
+
+    }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items/.openapi-generator-ignore b/samples/client/petstore/kotlin-array-nullable-items/.openapi-generator-ignore
new file mode 100644
index 000000000000..7484ee590a38
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/.openapi-generator-ignore
@@ -0,0 +1,23 @@
+# OpenAPI Generator Ignore
+# Generated by openapi-generator https://github.com/openapitools/openapi-generator
+
+# Use this file to prevent files from being overwritten by the generator.
+# The patterns follow closely to .gitignore or .dockerignore.
+
+# As an example, the C# client generator defines ApiClient.cs.
+# You can make changes and tell OpenAPI Generator to ignore just this file by uncommenting the following line:
+#ApiClient.cs
+
+# You can match any string of characters against a directory, file or extension with a single asterisk (*):
+#foo/*/qux
+# The above matches foo/bar/qux and foo/baz/qux, but not foo/bar/baz/qux
+
+# You can recursively match patterns against a directory, file or extension with a double asterisk (**):
+#foo/**/qux
+# This matches foo/bar/qux, foo/baz/qux, and foo/bar/baz/qux
+
+# You can also negate patterns with an exclamation (!).
+# For example, you can ignore all files in a docs folder with the file extension .md:
+#docs/*.md
+# Then explicitly reverse the ignore rule for a single file:
+#!docs/README.md
diff --git a/samples/client/petstore/kotlin-array-nullable-items/.openapi-generator/FILES b/samples/client/petstore/kotlin-array-nullable-items/.openapi-generator/FILES
new file mode 100644
index 000000000000..39fe24c105ab
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/.openapi-generator/FILES
@@ -0,0 +1,28 @@
+README.md
+build.gradle
+docs/ArrayWithNullableItemsModel.md
+docs/DefaultApi.md
+gradle/wrapper/gradle-wrapper.jar
+gradle/wrapper/gradle-wrapper.properties
+gradlew
+gradlew.bat
+settings.gradle
+src/main/kotlin/org/openapitools/client/apis/DefaultApi.kt
+src/main/kotlin/org/openapitools/client/infrastructure/ApiAbstractions.kt
+src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
+src/main/kotlin/org/openapitools/client/infrastructure/ApiResponse.kt
+src/main/kotlin/org/openapitools/client/infrastructure/BigDecimalAdapter.kt
+src/main/kotlin/org/openapitools/client/infrastructure/BigIntegerAdapter.kt
+src/main/kotlin/org/openapitools/client/infrastructure/ByteArrayAdapter.kt
+src/main/kotlin/org/openapitools/client/infrastructure/Errors.kt
+src/main/kotlin/org/openapitools/client/infrastructure/LocalDateAdapter.kt
+src/main/kotlin/org/openapitools/client/infrastructure/LocalDateTimeAdapter.kt
+src/main/kotlin/org/openapitools/client/infrastructure/OffsetDateTimeAdapter.kt
+src/main/kotlin/org/openapitools/client/infrastructure/PartConfig.kt
+src/main/kotlin/org/openapitools/client/infrastructure/RequestConfig.kt
+src/main/kotlin/org/openapitools/client/infrastructure/RequestMethod.kt
+src/main/kotlin/org/openapitools/client/infrastructure/ResponseExtensions.kt
+src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt
+src/main/kotlin/org/openapitools/client/infrastructure/URIAdapter.kt
+src/main/kotlin/org/openapitools/client/infrastructure/UUIDAdapter.kt
+src/main/kotlin/org/openapitools/client/models/ArrayWithNullableItemsModel.kt
diff --git a/samples/client/petstore/kotlin-array-nullable-items/.openapi-generator/VERSION b/samples/client/petstore/kotlin-array-nullable-items/.openapi-generator/VERSION
new file mode 100644
index 000000000000..ca7bf6e46889
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/.openapi-generator/VERSION
@@ -0,0 +1 @@
+7.23.0-SNAPSHOT
diff --git a/samples/client/petstore/kotlin-array-nullable-items/README.md b/samples/client/petstore/kotlin-array-nullable-items/README.md
new file mode 100644
index 000000000000..293251e725c0
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/README.md
@@ -0,0 +1,61 @@
+# org.openapitools.client - Kotlin client library for Kotlin client — nullable array items
+
+Regression spec for nullable items inside list/array properties.
+
+## Overview
+This API client was generated by the [OpenAPI Generator](https://openapi-generator.tech) project.  By using the [openapi-spec](https://github.com/OAI/OpenAPI-Specification) from a remote server, you can easily generate an API client.
+
+- API version: latest
+- Package version: 
+- Generator version: 7.23.0-SNAPSHOT
+- Build package: org.openapitools.codegen.languages.KotlinClientCodegen
+
+## Requires
+
+* Kotlin 2.2.20
+* Gradle 8.14
+
+## Build
+
+First, create the gradle wrapper script:
+
+```
+gradle wrapper
+```
+
+Then, run:
+
+```
+./gradlew check assemble
+```
+
+This runs all tests and packages the library.
+
+## Features/Implementation Notes
+
+* Supports JSON inputs/outputs, File inputs, and Form inputs.
+* Supports collection formats for query parameters: csv, tsv, ssv, pipes.
+* Some Kotlin and Java types are fully qualified to avoid conflicts with types defined in OpenAPI definitions.
+* Implementation of ApiClient is intended to reduce method counts, specifically to benefit Android targets.
+
+<a id="documentation-for-api-endpoints"></a>
+## Documentation for API Endpoints
+
+All URIs are relative to *http://localhost*
+
+| Class | Method | HTTP request | Description |
+| ------------ | ------------- | ------------- | ------------- |
+| *DefaultApi* | [**getModel**](docs/DefaultApi.md#getmodel) | **GET** / |  |
+
+
+<a id="documentation-for-models"></a>
+## Documentation for Models
+
+ - [org.openapitools.client.models.ArrayWithNullableItemsModel](docs/ArrayWithNullableItemsModel.md)
+
+
+<a id="documentation-for-authorization"></a>
+## Documentation for Authorization
+
+Endpoints do not require authorization.
+
diff --git a/samples/client/petstore/kotlin-array-nullable-items/build.gradle b/samples/client/petstore/kotlin-array-nullable-items/build.gradle
new file mode 100644
index 000000000000..54f27f1a99bb
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/build.gradle
@@ -0,0 +1,77 @@
+group 'org.openapitools'
+version '1.0.0'
+
+wrapper {
+    gradleVersion = '8.14.3'
+    distributionUrl = "https://services.gradle.org/distributions/gradle-$gradleVersion-all.zip"
+}
+
+buildscript {
+    ext.kotlin_version = '2.2.20'
+    ext.spotless_version = "7.2.1"
+
+    repositories {
+        maven { url "https://repo1.maven.org/maven2" }
+    }
+    dependencies {
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+        classpath "com.diffplug.spotless:spotless-plugin-gradle:$spotless_version"
+    }
+}
+
+apply plugin: 'kotlin'
+apply plugin: 'maven-publish'
+apply plugin: 'com.diffplug.spotless'
+
+repositories {
+    maven { url "https://repo1.maven.org/maven2" }
+}
+
+// Use spotless plugin to automatically format code, remove unused import, etc
+// To apply changes directly to the file, run `gradlew spotlessApply`
+// Ref: https://github.com/diffplug/spotless/tree/main/plugin-gradle
+spotless {
+    // comment out below to run spotless as part of the `check` task
+    enforceCheck false
+
+    format 'misc', {
+        // define the files (e.g. '*.gradle', '*.md') to apply `misc` to
+        target '.gitignore'
+
+        // define the steps to apply to those files
+        trimTrailingWhitespace()
+        indentWithSpaces() // Takes an integer argument if you don't like 4
+        endWithNewline()
+    }
+    kotlin {
+        ktfmt()
+    }
+}
+
+test {
+    useJUnitPlatform()
+}
+
+dependencies {
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
+    implementation "com.squareup.moshi:moshi-kotlin:1.15.2"
+    implementation "com.squareup.moshi:moshi-adapters:1.15.2"
+    implementation "com.squareup.okhttp3:okhttp:5.1.0"
+    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.4.2"
+}
+
+java {
+    withSourcesJar()
+}
+
+publishing {
+    publications {
+        maven(MavenPublication) {
+            groupId = 'org.openapitools'
+            artifactId = 'kotlin-array-nullable-items'
+            version = '1.0.0'
+            from components.java
+        }
+    }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items/docs/ArrayWithNullableItemsModel.md b/samples/client/petstore/kotlin-array-nullable-items/docs/ArrayWithNullableItemsModel.md
new file mode 100644
index 000000000000..b72190023de1
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/docs/ArrayWithNullableItemsModel.md
@@ -0,0 +1,11 @@
+
+# ArrayWithNullableItemsModel
+
+## Properties
+| Name | Type | Description | Notes |
+| ------------ | ------------- | ------------- | ------------- |
+| **requiredItems** | **kotlin.collections.List&lt;kotlin.String?&gt;** |  |  |
+| **optionalItems** | **kotlin.collections.List&lt;kotlin.String?&gt;** |  |  [optional] |
+
+
+
diff --git a/samples/client/petstore/kotlin-array-nullable-items/docs/DefaultApi.md b/samples/client/petstore/kotlin-array-nullable-items/docs/DefaultApi.md
new file mode 100644
index 000000000000..b0698436ab42
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/docs/DefaultApi.md
@@ -0,0 +1,50 @@
+# DefaultApi
+
+All URIs are relative to *http://localhost*
+
+| Method | HTTP request | Description |
+| ------------- | ------------- | ------------- |
+| [**getModel**](DefaultApi.md#getModel) | **GET** / |  |
+
+
+<a id="getModel"></a>
+# **getModel**
+> ArrayWithNullableItemsModel getModel()
+
+
+
+### Example
+```kotlin
+// Import classes:
+//import org.openapitools.client.infrastructure.*
+//import org.openapitools.client.models.*
+
+val apiInstance = DefaultApi()
+try {
+    val result : ArrayWithNullableItemsModel = apiInstance.getModel()
+    println(result)
+} catch (e: ClientException) {
+    println("4xx response calling DefaultApi#getModel")
+    e.printStackTrace()
+} catch (e: ServerException) {
+    println("5xx response calling DefaultApi#getModel")
+    e.printStackTrace()
+}
+```
+
+### Parameters
+This endpoint does not need any parameter.
+
+### Return type
+
+[**ArrayWithNullableItemsModel**](ArrayWithNullableItemsModel.md)
+
+### Authorization
+
+No authorization required
+
+### HTTP request headers
+
+ - **Content-Type**: Not defined
+ - **Accept**: application/json
+
diff --git a/samples/client/petstore/kotlin-array-nullable-items/gradle/wrapper/gradle-wrapper.jar b/samples/client/petstore/kotlin-array-nullable-items/gradle/wrapper/gradle-wrapper.jar
new file mode 100644
index 000000000000..2c3521197d7c
Binary files /dev/null and b/samples/client/petstore/kotlin-array-nullable-items/gradle/wrapper/gradle-wrapper.jar differ
diff --git a/samples/client/petstore/kotlin-array-nullable-items/gradle/wrapper/gradle-wrapper.properties b/samples/client/petstore/kotlin-array-nullable-items/gradle/wrapper/gradle-wrapper.properties
new file mode 100644
index 000000000000..7705927e949f
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/gradle/wrapper/gradle-wrapper.properties
@@ -0,0 +1,7 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.14.3-all.zip
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
diff --git a/samples/client/petstore/kotlin-array-nullable-items/gradlew b/samples/client/petstore/kotlin-array-nullable-items/gradlew
new file mode 100644
index 000000000000..51eb8bb47109
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/gradlew
@@ -0,0 +1,252 @@
+#!/bin/sh
+
+#
+# Copyright © 2015-2021 the original authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+##############################################################################
+#
+#   Gradle start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh Gradle
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/HEAD/platforms/jvm/plugins-application/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+[ -h "$app_path" ]
+do
+ls=$( ls -ld "$app_path" )
+link=${ls#*' -> '}
+case $link in             #(
+/*)   app_path=$link ;; #(
+*)    app_path=$APP_HOME$link ;;
+esac
+done
+
+# This is normally unused
+# shellcheck disable=SC2034
+APP_BASE_NAME=${0##*/}
+# Discard cd standard output in case $CDPATH is set (https://github.com/gradle/gradle/issues/25036)
+APP_HOME=$( cd -P "${APP_HOME:-./}" > /dev/null && printf '%s
+' "$PWD" ) || exit
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+echo "$*"
+} >&2
+
+die () {
+echo
+echo "$*"
+echo
+exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+CYGWIN* )         cygwin=true  ;; #(
+Darwin* )         darwin=true  ;; #(
+MSYS* | MINGW* )  msys=true    ;; #(
+NONSTOP* )        nonstop=true ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+# IBM's JDK on AIX uses strange locations for the executables
+JAVACMD=$JAVA_HOME/jre/sh/java
+else
+JAVACMD=$JAVA_HOME/bin/java
+fi
+if [ ! -x "$JAVACMD" ] ; then
+die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+else
+JAVACMD=java
+if ! command -v java >/dev/null 2>&1
+then
+die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+case $MAX_FD in #(
+max*)
+# In POSIX sh, ulimit -H is undefined. That's why the result is checked to see if it worked.
+# shellcheck disable=SC2039,SC3045
+MAX_FD=$( ulimit -H -n ) ||
+warn "Could not query maximum file descriptor limit"
+esac
+case $MAX_FD in  #(
+'' | soft) :;; #(
+*)
+# In POSIX sh, ulimit -n is undefined. That's why the result is checked to see if it worked.
+# shellcheck disable=SC2039,SC3045
+ulimit -n "$MAX_FD" ||
+warn "Could not set maximum file descriptor limit to $MAX_FD"
+esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
+
+JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+# Now convert the arguments - kludge to limit ourselves to /bin/sh
+for arg do
+if
+case $arg in                                #(
+-*)   false ;;                            # don't mess with options #(
+/?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+[ -e "$t" ] ;;                      #(
+*)    false ;;
+esac
+then
+arg=$( cygpath --path --ignore --mixed "$arg" )
+fi
+# Roll the args list around exactly as many times as the number of
+# args, so each arg winds up back in the position where it started, but
+# possibly modified.
+#
+# NB: a `for` loop captures its iteration list before it begins, so
+# changing the positional parameters here affects neither the number of
+# iterations, nor the values presented in `arg`.
+shift                   # remove old arg
+set -- "$@" "$arg"      # push replacement arg
+done
+fi
+
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Collect all arguments for the java command:
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, JAVA_OPTS, and optsEnvironmentVar are not allowed to contain shell fragments,
+#     and any embedded shellness will be escaped.
+#   * For example: A user cannot expect ${Hostname} to be expanded, as it is an environment variable and will be
+#     treated as '${Hostname}' itself on the command line.
+
+set -- \
+"-Dorg.gradle.appname=$APP_BASE_NAME" \
+-classpath "$CLASSPATH" \
+org.gradle.wrapper.GradleWrapperMain \
+"$@"
+
+# Stop when "xargs" is not available.
+if ! command -v xargs >/dev/null 2>&1
+then
+die "xargs is not available"
+fi
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+xargs -n1 |
+sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+tr '\n' ' '
+)" '"$@"'
+
+exec "$JAVACMD" "$@"
diff --git a/samples/client/petstore/kotlin-array-nullable-items/gradlew.bat b/samples/client/petstore/kotlin-array-nullable-items/gradlew.bat
new file mode 100644
index 000000000000..9d21a21834d5
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/gradlew.bat
@@ -0,0 +1,94 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+@rem SPDX-License-Identifier: Apache-2.0
+@rem
+
+@if "%DEBUG%"=="" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%"=="" set DIRNAME=.
+@rem This is normally unused
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if %ERRORLEVEL% equ 0 goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH. 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME% 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if %ERRORLEVEL% equ 0 goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+set EXIT_CODE=%ERRORLEVEL%
+if %EXIT_CODE% equ 0 set EXIT_CODE=1
+if not ""=="%GRADLE_EXIT_CONSOLE%" exit %EXIT_CODE%
+exit /b %EXIT_CODE%
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega
diff --git a/samples/client/petstore/kotlin-array-nullable-items/settings.gradle b/samples/client/petstore/kotlin-array-nullable-items/settings.gradle
new file mode 100644
index 000000000000..73ff4129acdf
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/settings.gradle
@@ -0,0 +1 @@
+rootProject.name = 'kotlin-array-nullable-items'
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/apis/DefaultApi.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/apis/DefaultApi.kt
new file mode 100644
index 000000000000..66b89498f839
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/apis/DefaultApi.kt
@@ -0,0 +1,129 @@
+/**
+ *
+ * Please note:
+ * This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+ * Do not edit this file manually.
+ *
+ */
+
+@file:Suppress(
+    "ArrayInDataClass",
+    "DuplicatedCode",
+    "EnumEntryName",
+    "RemoveRedundantQualifierName",
+    "RemoveRedundantCallsOfConversionMethods",
+    "REDUNDANT_CALL_OF_CONVERSION_METHOD",
+    "RedundantUnitReturnType",
+    "RemoveEmptyClassBody",
+    "UnnecessaryVariable",
+    "UnusedImport",
+    "UnnecessaryVariable",
+    "unused"
+)
+
+package org.openapitools.client.apis
+
+import java.io.IOException
+import okhttp3.Call
+import okhttp3.HttpUrl
+
+import org.openapitools.client.models.ArrayWithNullableItemsModel
+
+import com.squareup.moshi.Json
+
+import org.openapitools.client.infrastructure.ApiClient
+import org.openapitools.client.infrastructure.ApiResponse
+import org.openapitools.client.infrastructure.ClientException
+import org.openapitools.client.infrastructure.ClientError
+import org.openapitools.client.infrastructure.ServerException
+import org.openapitools.client.infrastructure.ServerError
+import org.openapitools.client.infrastructure.MultiValueMap
+import org.openapitools.client.infrastructure.PartConfig
+import org.openapitools.client.infrastructure.RequestConfig
+import org.openapitools.client.infrastructure.RequestMethod
+import org.openapitools.client.infrastructure.ResponseType
+import org.openapitools.client.infrastructure.Success
+import org.openapitools.client.infrastructure.toMultiValue
+
+open class DefaultApi(basePath: kotlin.String = defaultBasePath, client: Call.Factory = ApiClient.defaultClient) : ApiClient(basePath, client) {
+    companion object {
+        @JvmStatic
+        val defaultBasePath: String by lazy {
+            System.getProperties().getProperty(ApiClient.BASE_URL_KEY, "http://localhost")
+        }
+    }
+
+    /**
+     * GET /
+     * 
+     * 
+     * @return ArrayWithNullableItemsModel
+     * @throws IllegalStateException If the request is not correctly configured
+     * @throws IOException Rethrows the OkHttp execute method exception
+     * @throws UnsupportedOperationException If the API returns an informational or redirection response
+     * @throws ClientException If the API returns a client error response
+     * @throws ServerException If the API returns a server error response
+     */
+    @Suppress("UNCHECKED_CAST")
+    @Throws(IllegalStateException::class, IOException::class, UnsupportedOperationException::class, ClientException::class, ServerException::class)
+    fun getModel() : ArrayWithNullableItemsModel {
+        val localVarResponse = getModelWithHttpInfo()
+
+        return when (localVarResponse.responseType) {
+            ResponseType.Success -> (localVarResponse as Success<*>).data as ArrayWithNullableItemsModel
+            ResponseType.Informational -> throw UnsupportedOperationException("Client does not support Informational responses.")
+            ResponseType.Redirection -> throw UnsupportedOperationException("Client does not support Redirection responses.")
+            ResponseType.ClientError -> {
+                val localVarError = localVarResponse as ClientError<*>
+                throw ClientException("Client error : ${localVarError.statusCode} ${localVarError.message.orEmpty()}", localVarError.statusCode, localVarResponse)
+            }
+            ResponseType.ServerError -> {
+                val localVarError = localVarResponse as ServerError<*>
+                throw ServerException("Server error : ${localVarError.statusCode} ${localVarError.message.orEmpty()} ${localVarError.body}", localVarError.statusCode, localVarResponse)
+            }
+        }
+    }
+
+    /**
+     * GET /
+     * 
+     * 
+     * @return ApiResponse<ArrayWithNullableItemsModel?>
+     * @throws IllegalStateException If the request is not correctly configured
+     * @throws IOException Rethrows the OkHttp execute method exception
+     */
+    @Suppress("UNCHECKED_CAST")
+    @Throws(IllegalStateException::class, IOException::class)
+    fun getModelWithHttpInfo() : ApiResponse<ArrayWithNullableItemsModel?> {
+        val localVariableConfig = getModelRequestConfig()
+
+        return request<Unit, ArrayWithNullableItemsModel>(
+            localVariableConfig
+        )
+    }
+
+    /**
+     * To obtain the request config of the operation getModel
+     *
+     * @return RequestConfig
+     */
+    fun getModelRequestConfig() : RequestConfig<Unit> {
+        val localVariableBody = null
+        val localVariableQuery: MultiValueMap = mutableMapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
+        localVariableHeaders["Accept"] = "application/json"
+
+        return RequestConfig(
+            method = RequestMethod.GET,
+            path = "/",
+            query = localVariableQuery,
+            headers = localVariableHeaders,
+            requiresAuthentication = false,
+            body = localVariableBody
+        )
+    }
+
+
+    private fun encodeURIComponent(uriComponent: kotlin.String): kotlin.String =
+        HttpUrl.Builder().scheme("http").host("localhost").addPathSegment(uriComponent).build().encodedPathSegments[0]
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/ApiAbstractions.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/ApiAbstractions.kt
new file mode 100644
index 000000000000..7fe8da468374
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/ApiAbstractions.kt
@@ -0,0 +1,23 @@
+package org.openapitools.client.infrastructure
+
+typealias MultiValueMap = MutableMap<String,List<String>>
+
+fun collectionDelimiter(collectionFormat: String): String = when(collectionFormat) {
+    "csv" -> ","
+    "tsv" -> "\t"
+    "pipe" -> "|"
+    "space" -> " "
+    else -> ""
+}
+
+val defaultMultiValueConverter: (item: Any?) -> String = { item -> "$item" }
+
+fun <T : Any?> toMultiValue(items: Array<T>, collectionFormat: String, map: (item: T) -> String = defaultMultiValueConverter): List<String>
+        = toMultiValue(items.asIterable(), collectionFormat, map)
+
+fun <T : Any?> toMultiValue(items: Iterable<T>, collectionFormat: String, map: (item: T) -> String = defaultMultiValueConverter): List<String> {
+    return when(collectionFormat) {
+        "multi" -> items.map(map)
+        else -> listOf(items.joinToString(separator = collectionDelimiter(collectionFormat), transform = map))
+    }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
new file mode 100644
index 000000000000..0197390a824a
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
@@ -0,0 +1,467 @@
+package org.openapitools.client.infrastructure
+
+import okhttp3.OkHttpClient
+import okhttp3.RequestBody
+import okhttp3.RequestBody.Companion.asRequestBody
+import okhttp3.RequestBody.Companion.toRequestBody
+import okhttp3.FormBody
+import okhttp3.HttpUrl.Companion.toHttpUrlOrNull
+import okhttp3.ResponseBody
+import okhttp3.MediaType.Companion.toMediaTypeOrNull
+import okhttp3.Request
+import okhttp3.Headers
+import okhttp3.Headers.Builder
+import okhttp3.Headers.Companion.toHeaders
+import okhttp3.MultipartBody
+import okhttp3.Call
+import okhttp3.Callback
+import okhttp3.Response
+import java.io.BufferedWriter
+import java.io.File
+import java.io.FileWriter
+import java.io.IOException
+import java.net.URLConnection
+import java.time.LocalDate
+import java.time.LocalDateTime
+import java.time.LocalTime
+import java.time.OffsetDateTime
+import java.time.OffsetTime
+import java.util.Locale
+import java.util.regex.Pattern
+import com.squareup.moshi.adapter
+
+val EMPTY_REQUEST: RequestBody = ByteArray(0).toRequestBody()
+
+open class ApiClient(val baseUrl: String, val client: Call.Factory = defaultClient) {
+    companion object {
+        protected const val CONTENT_TYPE: String = "Content-Type"
+        @Deprecated(
+          message = "Please use the capitalized constant `CONTENT_TYPE` instead.",
+          replaceWith = ReplaceWith("CONTENT_TYPE")
+        )
+        protected const val ContentType: String = CONTENT_TYPE
+
+        protected const val ACCEPT: String = "Accept"
+        @Deprecated(
+          message = "Please use the capitalized constant `ACCEPT` instead.",
+          replaceWith = ReplaceWith("ACCEPT")
+        )
+        protected const val Accept: String = ACCEPT
+
+        protected const val AUTHORIZATION: String = "Authorization"
+        @Deprecated(
+          message = "Please use the capitalized constant `AUTHORIZATION` instead.",
+          replaceWith = ReplaceWith("AUTHORIZATION")
+        )
+        protected const val Authorization: String = AUTHORIZATION
+
+        protected const val JSON_MEDIA_TYPE: String = "application/json"
+        @Deprecated(
+          message = "Please use the capitalized constant `JSON_MEDIA_TYPE` instead.",
+          replaceWith = ReplaceWith("JSON_MEDIA_TYPE")
+        )
+        protected const val JsonMediaType: String = JSON_MEDIA_TYPE
+
+        protected const val FORM_DATA_MEDIA_TYPE: String = "multipart/form-data"
+        @Deprecated(
+          message = "Please use the capitalized constant `FORM_DATA_MEDIA_TYPE` instead.",
+          replaceWith = ReplaceWith("FORM_DATA_MEDIA_TYPE")
+        )
+        protected const val FormDataMediaType: String = FORM_DATA_MEDIA_TYPE
+
+        protected const val FORM_URL_ENC_MEDIA_TYPE: String = "application/x-www-form-urlencoded"
+        @Deprecated(
+          message = "Please use the capitalized constant `FORM_URL_ENC_MEDIA_TYPE` instead.",
+          replaceWith = ReplaceWith("FORM_URL_ENC_MEDIA_TYPE")
+        )
+        protected const val FormUrlEncMediaType: String = FORM_URL_ENC_MEDIA_TYPE
+
+        protected const val XML_MEDIA_TYPE: String = "application/xml"
+        @Deprecated(
+          message = "Please use the capitalized constant `XML_MEDIA_TYPE` instead.",
+          replaceWith = ReplaceWith("XML_MEDIA_TYPE")
+        )
+        protected const val XmlMediaType: String = XML_MEDIA_TYPE
+
+        protected const val OCTET_MEDIA_TYPE: String = "application/octet-stream"
+        @Deprecated(
+          message = "Please use the capitalized constant `OCTET_MEDIA_TYPE` instead.",
+          replaceWith = ReplaceWith("OCTET_MEDIA_TYPE")
+        )
+        protected const val OctetMediaType: String = OCTET_MEDIA_TYPE
+
+        protected const val TEXT_MEDIA_TYPE: String = "text/plain"
+        @Deprecated(
+          message = "Please use the capitalized constant `TEXT_MEDIA_TYPE` instead.",
+          replaceWith = ReplaceWith("TEXT_MEDIA_TYPE")
+        )
+        protected const val TextMediaType: String = TEXT_MEDIA_TYPE
+
+        const val BASE_URL_KEY: String = "org.openapitools.client.baseUrl"
+        @Deprecated(
+          message = "Please use the capitalized constant `BASE_URL_KEY` instead.",
+          replaceWith = ReplaceWith("BASE_URL_KEY")
+        )
+        const val baseUrlKey: String = BASE_URL_KEY
+
+        val apiKey: MutableMap<String, String> = mutableMapOf()
+        val apiKeyPrefix: MutableMap<String, String> = mutableMapOf()
+        var username: String? = null
+        var password: String? = null
+        var accessToken: String? = null
+
+        @JvmStatic
+        val defaultClient: OkHttpClient by lazy {
+            builder.build()
+        }
+
+        @JvmStatic
+        val builder: OkHttpClient.Builder = OkHttpClient.Builder()
+    }
+
+    /**
+     * Guess Content-Type header from the given byteArray (defaults to "application/octet-stream").
+     *
+     * @param byteArray The given file
+     * @return The guessed Content-Type
+     */
+    protected fun guessContentTypeFromByteArray(byteArray: ByteArray): String {
+        val contentType = try {
+            URLConnection.guessContentTypeFromStream(byteArray.inputStream())
+        } catch (_: IOException) {
+            "application/octet-stream"
+        }
+        return contentType
+    }
+
+    /**
+     * Guess Content-Type header from the given file (defaults to "application/octet-stream").
+     *
+     * @param file The given file
+     * @return The guessed Content-Type
+     */
+    protected fun guessContentTypeFromFile(file: File): String {
+        val contentType = URLConnection.guessContentTypeFromName(file.name)
+        return contentType ?: "application/octet-stream"
+    }
+
+    /**
+     * Builds headers for a multipart form-data part.
+     * OkHttp requires Content-Type to be passed via the RequestBody parameter, not in headers.
+     * This function filters out Content-Type and builds the appropriate Content-Disposition header.
+     *
+     * @param name The field name
+     * @param headers The headers from the PartConfig (may include Content-Type)
+     * @param filename Optional filename for file uploads
+     * @return Headers object ready for addPart()
+     */
+    protected fun buildPartHeaders(name: String, headers: Map<String, String>, filename: String? = null): Headers {
+        val disposition = if (filename != null) {
+            "form-data; name=\"$name\"; filename=\"$filename\""
+        } else {
+            "form-data; name=\"$name\""
+        }
+        return (headers.filterKeys { it != "Content-Type" } + ("Content-Disposition" to disposition)).toHeaders()
+    }
+
+    /**
+     * Adds a File to a MultipartBody.Builder
+     * Defined a helper in the requestBody method to not duplicate code
+     * It will be used when the content is a `FORM_DATA_MEDIA_TYPE` and the body of the PartConfig is a File
+     *
+     * @param name The field name to add in the request
+     * @param headers The headers that are in the PartConfig
+     * @param file The file that will be added as the field value
+     * @return The method returns Unit but the new Part is added to the Builder that the extension function is applying on
+     * @see requestBody
+     */
+    protected fun MultipartBody.Builder.addPartToMultiPart(name: String, headers: Map<String, String>, file: File) {
+        val fileMediaType = guessContentTypeFromFile(file).toMediaTypeOrNull()
+        addPart(
+            buildPartHeaders(name, headers, file.name),
+            file.asRequestBody(fileMediaType)
+        )
+    }
+
+    /**
+     * Serializes a multipart body part based on its content type.
+     * Uses JSON serialization for application/json content types, otherwise converts to string.
+     *
+     * @param obj The object to serialize
+     * @param contentType The Content-Type header value, if any
+     * @param serializer Optional custom serializer (used for kotlinx.serialization to preserve type info)
+     * @return The serialized string representation
+     */
+    protected fun serializePartBody(obj: Any?, contentType: String?, serializer: ((Any?) -> String)?): String {
+        // Use custom serializer if provided (for kotlinx.serialization with captured type info)
+        if (serializer != null) {
+            return serializer(obj)
+        }
+
+        return if (contentType?.contains("json") == true) {
+            Serializer.moshi.adapter(Any::class.java).toJson(obj)
+        } else {
+            parameterToString(obj)
+        }
+    }
+
+    /**
+     * Adds any type to a MultipartBody.Builder
+     * Defined a helper in the requestBody method to not duplicate code
+     * It will be used when the content is a `FORM_DATA_MEDIA_TYPE` and the body of the PartConfig is not a File.
+     *
+     * @param name The field name to add in the request
+     * @param headers The headers that are in the PartConfig
+     * @param obj The field name to add in the request
+     * @param serializer Optional custom serializer for this part
+     * @return The method returns Unit but the new Part is added to the Builder that the extension function is applying on
+     * @see requestBody
+     */
+    protected fun MultipartBody.Builder.addPartToMultiPart(name: String, headers: Map<String, String>, obj: Any?, serializer: ((Any?) -> String)? = null) {
+        val partContentType = headers["Content-Type"]
+        val partMediaType = partContentType?.toMediaTypeOrNull()
+        val partBody = serializePartBody(obj, partContentType, serializer)
+        addPart(
+            buildPartHeaders(name, headers),
+            partBody.toRequestBody(partMediaType)
+        )
+    }
+
+    protected inline fun <reified T> requestBody(content: T, mediaType: String?): RequestBody =
+        when {
+            content is ByteArray -> content.toRequestBody((mediaType ?: guessContentTypeFromByteArray(content)).toMediaTypeOrNull())
+            content is File -> content.asRequestBody((mediaType ?: guessContentTypeFromFile(content)).toMediaTypeOrNull())
+            mediaType == FORM_DATA_MEDIA_TYPE ->
+                MultipartBody.Builder()
+                    .setType(MultipartBody.FORM)
+                    .apply {
+                        // content's type *must* be Map<String, PartConfig<*>>
+                        @Suppress("UNCHECKED_CAST")
+                        (content as Map<String, PartConfig<*>>).forEach { (name, part) ->
+                            when (part.body) {
+                                is File -> addPartToMultiPart(name, part.headers, part.body)
+                                is List<*> -> {
+                                    part.body.forEach {
+                                        if (it is File) {
+                                            addPartToMultiPart(name, part.headers, it)
+                                        } else {
+                                            addPartToMultiPart(name, part.headers, it, part.serializer)
+                                        }
+                                    }
+                               }
+                               else -> addPartToMultiPart(name, part.headers, part.body, part.serializer)
+                            }
+                        }
+                    }.build()
+            mediaType == FORM_URL_ENC_MEDIA_TYPE -> {
+                FormBody.Builder().apply {
+                    // content's type *must* be Map<String, PartConfig<*>>
+                    @Suppress("UNCHECKED_CAST")
+                    (content as Map<String, PartConfig<*>>).forEach { (name, part) ->
+                        add(name, parameterToString(part.body))
+                    }
+                }.build()
+            }
+            mediaType == null || mediaType.startsWith("application/") && mediaType.endsWith("json") ->
+                if (content == null) {
+                    EMPTY_REQUEST
+                } else {
+                    Serializer.moshi.adapter(T::class.java).toJson(content)
+                        .toRequestBody((mediaType ?: JSON_MEDIA_TYPE).toMediaTypeOrNull())
+                }
+            mediaType == XML_MEDIA_TYPE -> throw UnsupportedOperationException("xml not currently supported.")
+            mediaType == TEXT_MEDIA_TYPE -> {
+                val textualContent = when (content) {
+                    is Char, is CharSequence -> content.toString()
+                    is Number -> content.toString()
+                    is Boolean -> content.toString()
+                    else -> throw UnsupportedOperationException("requestBody currently only supports text body containing primitive types: characters, numbers, or booleans.")
+                }
+                textualContent.toRequestBody(mediaType.toMediaTypeOrNull())
+            }
+            // TODO: this should be extended with other serializers
+            else -> throw UnsupportedOperationException("requestBody currently only supports JSON body, text body, byte body and File body.")
+        }
+
+    @OptIn(ExperimentalStdlibApi::class)
+    protected inline fun <reified T: Any?> responseBody(response: Response, mediaType: String? = JSON_MEDIA_TYPE): T? {
+        val body = response.body ?: return null
+
+        if (T::class.java == Unit::class.java) {
+            // No need to parse the body when we're not interested in the body
+            // Useful when API is returning other Content-Type
+            return null
+        } else if (T::class.java == File::class.java) {
+            // return tempFile
+            val contentDisposition = response.header("Content-Disposition")
+
+            val fileName = if (contentDisposition != null) {
+                // Get filename from the Content-Disposition header.
+                val pattern = Pattern.compile("filename=['\"]?([^'\"\\s]+)['\"]?")
+                val matcher = pattern.matcher(contentDisposition)
+                if (matcher.find()) {
+                    matcher.group(1)
+                        ?.replace(".*[/\\\\]", "")
+                        ?.replace(";", "")
+                } else {
+                    null
+                }
+            } else {
+                null
+            }
+
+            var prefix: String?
+            val suffix: String?
+            if (fileName == null) {
+                prefix = "download"
+                suffix = ""
+            } else {
+                val pos = fileName.lastIndexOf(".")
+                if (pos == -1) {
+                    prefix = fileName
+                    suffix = null
+                } else {
+                    prefix = fileName.substring(0, pos)
+                    suffix = fileName.substring(pos)
+                }
+                // Files.createTempFile requires the prefix to be at least three characters long
+                if (prefix.length < 3) {
+                    prefix = "download"
+                }
+            }
+
+            // Attention: if you are developing an android app that supports API Level 25 and below, please check flag supportAndroidApiLevel25AndBelow in https://openapi-generator.tech/docs/generators/kotlin#config-options
+            val tempFile = java.nio.file.Files.createTempFile(prefix, suffix).toFile()
+            tempFile.deleteOnExit()
+            body.byteStream().use { inputStream ->
+                tempFile.outputStream().use { tempFileOutputStream ->
+                    inputStream.copyTo(tempFileOutputStream)
+                }
+            }
+            return tempFile as T
+        }
+
+        return when {
+            mediaType == null || (mediaType.startsWith("application/") && mediaType.endsWith("json")) -> {
+                val bodyContent = body.string()
+                if (bodyContent.isEmpty()) {
+                    return null
+                }
+                Serializer.moshi.adapter<T>().fromJson(bodyContent)
+            }
+            mediaType == OCTET_MEDIA_TYPE -> body.bytes() as? T
+            mediaType == TEXT_MEDIA_TYPE -> body.string() as? T
+            else ->  throw UnsupportedOperationException("responseBody currently only supports JSON body, text body and byte body.")
+        }
+    }
+
+
+    protected inline fun <reified I, reified T: Any?> request(requestConfig: RequestConfig<I>): ApiResponse<T?> {
+        val httpUrl = baseUrl.toHttpUrlOrNull() ?: throw IllegalStateException("baseUrl is invalid.")
+
+        val url = httpUrl.newBuilder()
+            .addEncodedPathSegments(requestConfig.path.trimStart('/'))
+            .apply {
+                requestConfig.query.forEach { query ->
+                    query.value.forEach { queryValue ->
+                        addQueryParameter(query.key, queryValue)
+                    }
+                }
+            }.build()
+
+        // take content-type/accept from spec or set to default (application/json) if not defined
+        if (requestConfig.body != null && requestConfig.headers[CONTENT_TYPE].isNullOrEmpty()) {
+            requestConfig.headers[CONTENT_TYPE] = JSON_MEDIA_TYPE
+        }
+        if (requestConfig.headers[ACCEPT].isNullOrEmpty()) {
+            requestConfig.headers[ACCEPT] = JSON_MEDIA_TYPE
+        }
+        val headers = requestConfig.headers
+
+        if (headers[ACCEPT].isNullOrEmpty()) {
+            throw kotlin.IllegalStateException("Missing ACCEPT header. This is required.")
+        }
+
+        val contentType = if (headers[CONTENT_TYPE] != null) {
+            // TODO: support multiple contentType options here.
+            (headers[CONTENT_TYPE] as String).substringBefore(";").lowercase(Locale.US)
+        } else {
+            null
+        }
+
+        val request = when (requestConfig.method) {
+            RequestMethod.DELETE -> Request.Builder().url(url).delete(requestBody(requestConfig.body, contentType))
+            RequestMethod.GET -> Request.Builder().url(url)
+            RequestMethod.HEAD -> Request.Builder().url(url).head()
+            RequestMethod.PATCH -> Request.Builder().url(url).patch(requestBody(requestConfig.body, contentType))
+            RequestMethod.PUT -> Request.Builder().url(url).put(requestBody(requestConfig.body, contentType))
+            RequestMethod.POST -> Request.Builder().url(url).post(requestBody(requestConfig.body, contentType))
+            RequestMethod.OPTIONS -> Request.Builder().url(url).method("OPTIONS", null)
+        }.apply {
+            val headersBuilder = Headers.Builder()
+            headers.forEach { header ->
+                headersBuilder.add(header.key, header.value)
+            }
+            this.headers(headersBuilder.build())
+        }.build()
+
+        val response = client.newCall(request).execute()
+
+        val accept = response.header(CONTENT_TYPE)?.substringBefore(";")?.lowercase(Locale.US)
+
+        // TODO: handle specific mapping types. e.g. Map<int, Class<?>>
+        @Suppress("UNNECESSARY_SAFE_CALL")
+        return response.use {
+            when {
+                it.isRedirect -> Redirection(
+                    it.code,
+                    it.headers.toMultimap()
+                )
+                it.isInformational -> Informational(
+                    it.message,
+                    it.code,
+                    it.headers.toMultimap()
+                )
+                it.isSuccessful -> Success(
+                    responseBody(it, accept),
+                    it.code,
+                    it.headers.toMultimap()
+                )
+                it.isClientError -> ClientError(
+                    it.message,
+                    it.body?.string(),
+                    it.code,
+                    it.headers.toMultimap()
+                )
+                else -> ServerError(
+                    it.message,
+                    it.body?.string(),
+                    it.code,
+                    it.headers.toMultimap()
+                )
+            }
+        }
+    }
+
+    protected fun parameterToString(value: Any?): String = when (value) {
+        null -> ""
+        is Array<*> -> toMultiValue(value, "csv").toString()
+        is Iterable<*> -> toMultiValue(value, "csv").toString()
+        is OffsetDateTime -> parseDateToQueryString<OffsetDateTime>(value)
+        is OffsetTime -> parseDateToQueryString<OffsetTime>(value)
+        is LocalDateTime -> parseDateToQueryString<LocalDateTime>(value)
+        is LocalDate -> parseDateToQueryString<LocalDate>(value)
+        is LocalTime -> parseDateToQueryString<LocalTime>(value)
+        else -> value.toString()
+    }
+
+    protected inline fun <reified T: Any> parseDateToQueryString(value : T): String {
+        /*
+        .replace("\"", "") converts the json object string to an actual string for the query parameter.
+        The moshi or gson adapter allows a more generic solution instead of trying to use a native
+        formatter. It also easily allows to provide a simple way to define a custom date format pattern
+        inside a gson/moshi adapter.
+        */
+        return Serializer.moshi.adapter(T::class.java).toJson(value).replace("\"", "")
+    }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/ApiResponse.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/ApiResponse.kt
new file mode 100644
index 000000000000..689fb03cd7ae
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/ApiResponse.kt
@@ -0,0 +1,43 @@
+package org.openapitools.client.infrastructure
+
+enum class ResponseType {
+    Success, Informational, Redirection, ClientError, ServerError
+}
+
+interface Response
+
+abstract class ApiResponse<T>(val responseType: ResponseType): Response {
+    abstract val statusCode: Int
+    abstract val headers: Map<String,List<String>>
+}
+
+class Success<T>(
+    val data: T,
+    override val statusCode: Int = -1,
+    override val headers: Map<String, List<String>> = mapOf()
+): ApiResponse<T>(ResponseType.Success)
+
+class Informational<T>(
+    val statusText: String,
+    override val statusCode: Int = -1,
+    override val headers: Map<String, List<String>> = mapOf()
+) : ApiResponse<T>(ResponseType.Informational)
+
+class Redirection<T>(
+    override val statusCode: Int = -1,
+    override val headers: Map<String, List<String>> = mapOf()
+) : ApiResponse<T>(ResponseType.Redirection)
+
+class ClientError<T>(
+    val message: String? = null,
+    val body: Any? = null,
+    override val statusCode: Int = -1,
+    override val headers: Map<String, List<String>> = mapOf()
+) : ApiResponse<T>(ResponseType.ClientError)
+
+class ServerError<T>(
+    val message: String? = null,
+    val body: Any? = null,
+    override val statusCode: Int = -1,
+    override val headers: Map<String, List<String>> = mapOf()
+): ApiResponse<T>(ResponseType.ServerError)
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/BigDecimalAdapter.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/BigDecimalAdapter.kt
new file mode 100644
index 000000000000..064b57fc6b82
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/BigDecimalAdapter.kt
@@ -0,0 +1,17 @@
+package org.openapitools.client.infrastructure
+
+import com.squareup.moshi.FromJson
+import com.squareup.moshi.ToJson
+import java.math.BigDecimal
+
+class BigDecimalAdapter {
+    @ToJson
+    fun toJson(value: BigDecimal): String {
+        return value.toPlainString()
+    }
+
+    @FromJson
+    fun fromJson(value: String): BigDecimal {
+        return BigDecimal(value)
+    }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/BigIntegerAdapter.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/BigIntegerAdapter.kt
new file mode 100644
index 000000000000..7df6057b4503
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/BigIntegerAdapter.kt
@@ -0,0 +1,17 @@
+package org.openapitools.client.infrastructure
+
+import com.squareup.moshi.FromJson
+import com.squareup.moshi.ToJson
+import java.math.BigInteger
+
+class BigIntegerAdapter {
+    @ToJson
+    fun toJson(value: BigInteger): String {
+        return value.toString()
+    }
+
+    @FromJson
+    fun fromJson(value: String): BigInteger {
+        return BigInteger(value)
+    }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/ByteArrayAdapter.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/ByteArrayAdapter.kt
new file mode 100644
index 000000000000..ff5e2a81ee8c
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/ByteArrayAdapter.kt
@@ -0,0 +1,12 @@
+package org.openapitools.client.infrastructure
+
+import com.squareup.moshi.FromJson
+import com.squareup.moshi.ToJson
+
+class ByteArrayAdapter {
+    @ToJson
+    fun toJson(data: ByteArray): String = String(data)
+
+    @FromJson
+    fun fromJson(data: String): ByteArray = data.toByteArray()
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/Errors.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/Errors.kt
new file mode 100644
index 000000000000..c83993b9055c
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/Errors.kt
@@ -0,0 +1,18 @@
+@file:Suppress("unused")
+package org.openapitools.client.infrastructure
+
+import java.lang.RuntimeException
+
+open class ClientException(message: kotlin.String? = null, val statusCode: Int = -1, val response: Response? = null) : RuntimeException(message) {
+
+    companion object {
+        private const val serialVersionUID: Long = 123L
+    }
+}
+
+open class ServerException(message: kotlin.String? = null, val statusCode: Int = -1, val response: Response? = null) : RuntimeException(message) {
+
+    companion object {
+        private const val serialVersionUID: Long = 456L
+    }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/LocalDateAdapter.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/LocalDateAdapter.kt
new file mode 100644
index 000000000000..b2e1654479a0
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/LocalDateAdapter.kt
@@ -0,0 +1,19 @@
+package org.openapitools.client.infrastructure
+
+import com.squareup.moshi.FromJson
+import com.squareup.moshi.ToJson
+import java.time.LocalDate
+import java.time.format.DateTimeFormatter
+
+class LocalDateAdapter {
+    @ToJson
+    fun toJson(value: LocalDate): String {
+        return DateTimeFormatter.ISO_LOCAL_DATE.format(value)
+    }
+
+    @FromJson
+    fun fromJson(value: String): LocalDate {
+        return LocalDate.parse(value, DateTimeFormatter.ISO_LOCAL_DATE)
+    }
+
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/LocalDateTimeAdapter.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/LocalDateTimeAdapter.kt
new file mode 100644
index 000000000000..e082db94811d
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/LocalDateTimeAdapter.kt
@@ -0,0 +1,19 @@
+package org.openapitools.client.infrastructure
+
+import com.squareup.moshi.FromJson
+import com.squareup.moshi.ToJson
+import java.time.LocalDateTime
+import java.time.format.DateTimeFormatter
+
+class LocalDateTimeAdapter {
+    @ToJson
+    fun toJson(value: LocalDateTime): String {
+        return DateTimeFormatter.ISO_LOCAL_DATE_TIME.format(value)
+    }
+
+    @FromJson
+    fun fromJson(value: String): LocalDateTime {
+        return LocalDateTime.parse(value, DateTimeFormatter.ISO_LOCAL_DATE_TIME)
+    }
+
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/OffsetDateTimeAdapter.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/OffsetDateTimeAdapter.kt
new file mode 100644
index 000000000000..87437871a31e
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/OffsetDateTimeAdapter.kt
@@ -0,0 +1,19 @@
+package org.openapitools.client.infrastructure
+
+import com.squareup.moshi.FromJson
+import com.squareup.moshi.ToJson
+import java.time.OffsetDateTime
+import java.time.format.DateTimeFormatter
+
+class OffsetDateTimeAdapter {
+    @ToJson
+    fun toJson(value: OffsetDateTime): String {
+        return DateTimeFormatter.ISO_OFFSET_DATE_TIME.format(value)
+    }
+
+    @FromJson
+    fun fromJson(value: String): OffsetDateTime {
+        return OffsetDateTime.parse(value, DateTimeFormatter.ISO_OFFSET_DATE_TIME)
+    }
+
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/PartConfig.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/PartConfig.kt
new file mode 100644
index 000000000000..c2a5c99ec7e6
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/PartConfig.kt
@@ -0,0 +1,19 @@
+package org.openapitools.client.infrastructure
+
+/**
+ * Defines a config object for a given part of a multi-part request.
+ * NOTE: Headers is a Map<String,String> because rfc2616 defines
+ *       multi-valued headers as csv-only.
+ * 
+ * @property headers The headers for this part
+ * @property body The body content for this part
+ * @property serializer Optional custom serializer for JSON content. When provided, this will be
+ *                      used instead of the default serialization for parts with application/json
+ *                      content-type. This allows capturing type information at the call site to
+ *                      avoid issues with type erasure in kotlinx.serialization.
+ */
+data class PartConfig<T>(
+    val headers: MutableMap<String, String> = mutableMapOf(),
+    val body: T? = null,
+    val serializer: ((Any?) -> String)? = null
+)
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/RequestConfig.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/RequestConfig.kt
new file mode 100644
index 000000000000..6578b9381b78
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/RequestConfig.kt
@@ -0,0 +1,19 @@
+package org.openapitools.client.infrastructure
+
+/**
+ * Defines a config object for a given request.
+ * NOTE: This object doesn't include 'body' because it
+ *       allows for caching of the constructed object
+ *       for many request definitions.
+ * NOTE: Headers is a Map<String,String> because rfc2616 defines
+ *       multi-valued headers as csv-only.
+ */
+data class RequestConfig<T>(
+    val method: RequestMethod,
+    val path: String,
+    val headers: MutableMap<String, String> = mutableMapOf(),
+    val params: MutableMap<String, Any> = mutableMapOf(),
+    val query: MutableMap<String, List<String>> = mutableMapOf(),
+    val requiresAuthentication: Boolean,
+    val body: T? = null
+)
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/RequestMethod.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/RequestMethod.kt
new file mode 100644
index 000000000000..beb56f07cdde
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/RequestMethod.kt
@@ -0,0 +1,8 @@
+package org.openapitools.client.infrastructure
+
+/**
+ * Provides enumerated HTTP verbs
+ */
+enum class RequestMethod {
+    GET, DELETE, HEAD, OPTIONS, PATCH, POST, PUT
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/ResponseExtensions.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/ResponseExtensions.kt
new file mode 100644
index 000000000000..9bd2790dc144
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/ResponseExtensions.kt
@@ -0,0 +1,24 @@
+package org.openapitools.client.infrastructure
+
+import okhttp3.Response
+
+/**
+ * Provides an extension to evaluation whether the response is a 1xx code
+ */
+val Response.isInformational : Boolean get() = this.code in 100..199
+
+/**
+ * Provides an extension to evaluation whether the response is a 3xx code
+ */
+@Suppress("EXTENSION_SHADOWED_BY_MEMBER")
+val Response.isRedirect : Boolean get() = this.code in 300..399
+
+/**
+ * Provides an extension to evaluation whether the response is a 4xx code
+ */
+val Response.isClientError : Boolean get() = this.code in 400..499
+
+/**
+ * Provides an extension to evaluation whether the response is a 5xx (Standard) through 999 (non-standard) code
+ */
+val Response.isServerError : Boolean get() = this.code in 500..999
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt
new file mode 100644
index 000000000000..e22592e47d74
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt
@@ -0,0 +1,23 @@
+package org.openapitools.client.infrastructure
+
+import com.squareup.moshi.Moshi
+import com.squareup.moshi.kotlin.reflect.KotlinJsonAdapterFactory
+
+object Serializer {
+    @JvmStatic
+    val moshiBuilder: Moshi.Builder = Moshi.Builder()
+        .add(OffsetDateTimeAdapter())
+        .add(LocalDateTimeAdapter())
+        .add(LocalDateAdapter())
+        .add(UUIDAdapter())
+        .add(ByteArrayAdapter())
+        .add(URIAdapter())
+        .add(KotlinJsonAdapterFactory())
+        .add(BigDecimalAdapter())
+        .add(BigIntegerAdapter())
+
+    @JvmStatic
+    val moshi: Moshi by lazy {
+        moshiBuilder.build()
+    }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/URIAdapter.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/URIAdapter.kt
new file mode 100644
index 000000000000..979301f7a030
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/URIAdapter.kt
@@ -0,0 +1,13 @@
+package org.openapitools.client.infrastructure
+
+import com.squareup.moshi.FromJson
+import com.squareup.moshi.ToJson
+import java.net.URI
+
+class URIAdapter {
+    @ToJson
+    fun toJson(uri: URI): String = uri.toString()
+
+    @FromJson
+    fun fromJson(s: String): URI = URI.create(s)
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/UUIDAdapter.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/UUIDAdapter.kt
new file mode 100644
index 000000000000..d050ce08f76f
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/infrastructure/UUIDAdapter.kt
@@ -0,0 +1,13 @@
+package org.openapitools.client.infrastructure
+
+import com.squareup.moshi.FromJson
+import com.squareup.moshi.ToJson
+import java.util.UUID
+
+class UUIDAdapter {
+    @ToJson
+    fun toJson(uuid: UUID): String = uuid.toString()
+
+    @FromJson
+    fun fromJson(s: String): UUID = UUID.fromString(s)
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/models/ArrayWithNullableItemsModel.kt b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/models/ArrayWithNullableItemsModel.kt
new file mode 100644
index 000000000000..9772cb235ae4
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/main/kotlin/org/openapitools/client/models/ArrayWithNullableItemsModel.kt
@@ -0,0 +1,50 @@
+/**
+ *
+ * Please note:
+ * This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+ * Do not edit this file manually.
+ *
+ */
+
+@file:Suppress(
+    "ArrayInDataClass",
+    "DuplicatedCode",
+    "EnumEntryName",
+    "RemoveRedundantQualifierName",
+    "RemoveRedundantCallsOfConversionMethods",
+    "REDUNDANT_CALL_OF_CONVERSION_METHOD",
+    "RedundantUnitReturnType",
+    "RemoveEmptyClassBody",
+    "UnnecessaryVariable",
+    "UnusedImport",
+    "UnnecessaryVariable",
+    "unused"
+)
+
+package org.openapitools.client.models
+
+
+import com.squareup.moshi.Json
+import com.squareup.moshi.JsonClass
+
+/**
+ * 
+ *
+ * @param requiredItems 
+ * @param optionalItems 
+ */
+
+
+data class ArrayWithNullableItemsModel (
+
+    @Json(name = "requiredItems")
+    val requiredItems: kotlin.collections.List<kotlin.String?>,
+
+    @Json(name = "optionalItems")
+    val optionalItems: kotlin.collections.List<kotlin.String?>? = null
+
+) {
+
+
+}
+
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/test/kotlin/org/openapitools/client/apis/DefaultApiTest.kt b/samples/client/petstore/kotlin-array-nullable-items/src/test/kotlin/org/openapitools/client/apis/DefaultApiTest.kt
new file mode 100644
index 000000000000..d2700e179dd5
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/test/kotlin/org/openapitools/client/apis/DefaultApiTest.kt
@@ -0,0 +1,45 @@
+/**
+ *
+ * Please note:
+ * This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+ * Do not edit this file manually.
+ *
+ */
+
+@file:Suppress(
+    "ArrayInDataClass",
+    "DuplicatedCode",
+    "EnumEntryName",
+    "RemoveRedundantQualifierName",
+    "RemoveRedundantCallsOfConversionMethods",
+    "REDUNDANT_CALL_OF_CONVERSION_METHOD",
+    "RedundantUnitReturnType",
+    "RemoveEmptyClassBody",
+    "UnnecessaryVariable",
+    "UnusedImport",
+    "UnnecessaryVariable",
+    "unused"
+)
+
+package org.openapitools.client.apis
+
+import io.kotlintest.shouldBe
+import io.kotlintest.specs.ShouldSpec
+
+import org.openapitools.client.apis.DefaultApi
+import org.openapitools.client.models.ArrayWithNullableItemsModel
+
+class DefaultApiTest : ShouldSpec() {
+    init {
+        // uncomment below to create an instance of DefaultApi
+        //val apiInstance = DefaultApi()
+
+        // to test getModel
+        should("test getModel") {
+            // uncomment below to test getModel
+            //val result : ArrayWithNullableItemsModel = apiInstance.getModel()
+            //result shouldBe ("TODO")
+        }
+
+    }
+}
diff --git a/samples/client/petstore/kotlin-array-nullable-items/src/test/kotlin/org/openapitools/client/models/ArrayWithNullableItemsModelTest.kt b/samples/client/petstore/kotlin-array-nullable-items/src/test/kotlin/org/openapitools/client/models/ArrayWithNullableItemsModelTest.kt
new file mode 100644
index 000000000000..c99c9d5e8b92
--- /dev/null
+++ b/samples/client/petstore/kotlin-array-nullable-items/src/test/kotlin/org/openapitools/client/models/ArrayWithNullableItemsModelTest.kt
@@ -0,0 +1,49 @@
+/**
+ *
+ * Please note:
+ * This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+ * Do not edit this file manually.
+ *
+ */
+
+@file:Suppress(
+    "ArrayInDataClass",
+    "DuplicatedCode",
+    "EnumEntryName",
+    "RemoveRedundantQualifierName",
+    "RemoveRedundantCallsOfConversionMethods",
+    "REDUNDANT_CALL_OF_CONVERSION_METHOD",
+    "RedundantUnitReturnType",
+    "RemoveEmptyClassBody",
+    "UnnecessaryVariable",
+    "UnusedImport",
+    "UnnecessaryVariable",
+    "unused"
+)
+
+package org.openapitools.client.models
+
+import io.kotlintest.shouldBe
+import io.kotlintest.specs.ShouldSpec
+
+import org.openapitools.client.models.ArrayWithNullableItemsModel
+
+class ArrayWithNullableItemsModelTest : ShouldSpec() {
+    init {
+        // uncomment below to create an instance of ArrayWithNullableItemsModel
+        //val modelInstance = ArrayWithNullableItemsModel()
+
+        // to test the property `requiredItems`
+        should("test requiredItems") {
+            // uncomment below to test the property
+            //modelInstance.requiredItems shouldBe ("TODO")
+        }
+
+        // to test the property `optionalItems`
+        should("test optionalItems") {
+            // uncomment below to test the property
+            //modelInstance.optionalItems shouldBe ("TODO")
+        }
+
+    }
+}