fix(http-client-java): handle null LRO error response bodies (#11007)

downstream Azure/azure-sdk-for-java#49537

## Summary
- default generated management LRO error response bodies to an empty
byte array when the service returns no body
- add a management template test covering the generated HttpResponseImpl
output
- regenerate the affected management test clients and add a changelog
entry

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: weidongxu-microsoft

.chronus/changes/fix-http-client-java-lro-empty-body-2026-6-17-15-59-00.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http-client-java"
+---
+
+Fix null LRO error response body handling in generated management clients.

packages/http-client-java/generator/http-client-generator-mgmt/src/main/java/com/microsoft/typespec/http/client/generator/mgmt/template/FluentServiceClientTemplate.java

@@ -133,8 +133,10 @@ protected void writeAdditionalClassBlock(JavaClass classBlock) {
                         code.line("super(null);");
                         code.line("this.statusCode = statusCode;");
                         code.line("this.httpHeaders = httpHeaders;");
+                        // Use an empty array so body accessors still work when the poller surfaces an error without a
+                        // response body.
                         code.line(
-                            "this.responseBody = responseBody == null ? null : responseBody.getBytes(StandardCharsets.UTF_8);");
+                            "this.responseBody = responseBody == null ? new byte[0] : responseBody.getBytes(StandardCharsets.UTF_8);");
                     });
 
                 block.publicMethod("int getStatusCode()", code -> code.methodReturn("statusCode"));

packages/http-client-java/generator/http-client-generator-mgmt/src/test/java/com/microsoft/typespec/http/client/generator/mgmt/template/FluentServiceClientTemplateTests.java

@@ -0,0 +1,33 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+package com.microsoft.typespec.http.client.generator.mgmt.template;
+
+import com.microsoft.typespec.http.client.generator.core.model.javamodel.JavaFile;
+import com.microsoft.typespec.http.client.generator.mgmt.TestUtils;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+public class FluentServiceClientTemplateTests {
+
+    @BeforeAll
+    public static void ensurePlugin() {
+        new TestUtils.MockFluentGen();
+    }
+
+    @Test
+    public void writesEmptyByteArrayForNullLroErrorBody() {
+        JavaFile javaFile = new JavaFile("ProgramEnrollmentManagementClientImpl.java");
+
+        javaFile.publicFinalClass("ProgramEnrollmentManagementClientImpl",
+            classBlock -> FluentServiceClientTemplate.getInstance().writeAdditionalClassBlock(classBlock));
+
+        String output = javaFile.getContents().toString();
+
+        Assertions.assertTrue(output.contains(
+            "this.responseBody = responseBody == null ? new byte[0] : responseBody.getBytes(StandardCharsets.UTF_8);"));
+        Assertions.assertFalse(output.contains(
+            "this.responseBody = responseBody == null ? null : responseBody.getBytes(StandardCharsets.UTF_8);"));
+    }
+}

packages/http-client-java/generator/http-client-generator-test/src/main/java/azure/resourcemanager/commonproperties/implementation/CommonPropertiesClientImpl.java

@@ -304,7 +304,7 @@ private static final class HttpResponseImpl extends HttpResponse {
             super(null);
             this.statusCode = statusCode;
             this.httpHeaders = httpHeaders;
-            this.responseBody = responseBody == null ? null : responseBody.getBytes(StandardCharsets.UTF_8);
+            this.responseBody = responseBody == null ? new byte[0] : responseBody.getBytes(StandardCharsets.UTF_8);
         }
 
         public int getStatusCode() {

packages/http-client-java/generator/http-client-generator-test/src/main/java/azure/resourcemanager/largeheader/implementation/LargeHeaderClientImpl.java

@@ -272,7 +272,7 @@ private static final class HttpResponseImpl extends HttpResponse {
             super(null);
             this.statusCode = statusCode;
             this.httpHeaders = httpHeaders;
-            this.responseBody = responseBody == null ? null : responseBody.getBytes(StandardCharsets.UTF_8);
+            this.responseBody = responseBody == null ? new byte[0] : responseBody.getBytes(StandardCharsets.UTF_8);
         }
 
         public int getStatusCode() {

packages/http-client-java/generator/http-client-generator-test/src/main/java/azure/resourcemanager/managementgroup/implementation/ManagementGroupClientImpl.java

@@ -256,7 +256,7 @@ private static final class HttpResponseImpl extends HttpResponse {
             super(null);
             this.statusCode = statusCode;
             this.httpHeaders = httpHeaders;
-            this.responseBody = responseBody == null ? null : responseBody.getBytes(StandardCharsets.UTF_8);
+            this.responseBody = responseBody == null ? new byte[0] : responseBody.getBytes(StandardCharsets.UTF_8);
         }
 
         public int getStatusCode() {

packages/http-client-java/generator/http-client-generator-test/src/main/java/azure/resourcemanager/methodsubscriptionid/implementation/MethodSubscriptionIdClientImpl.java

@@ -346,7 +346,7 @@ private static final class HttpResponseImpl extends HttpResponse {
             super(null);
             this.statusCode = statusCode;
             this.httpHeaders = httpHeaders;
-            this.responseBody = responseBody == null ? null : responseBody.getBytes(StandardCharsets.UTF_8);
+            this.responseBody = responseBody == null ? new byte[0] : responseBody.getBytes(StandardCharsets.UTF_8);
         }
 
         public int getStatusCode() {

packages/http-client-java/generator/http-client-generator-test/src/main/java/azure/resourcemanager/multiservice/combined/implementation/CombinedImpl.java

@@ -273,7 +273,7 @@ private static final class HttpResponseImpl extends HttpResponse {
             super(null);
             this.statusCode = statusCode;
             this.httpHeaders = httpHeaders;
-            this.responseBody = responseBody == null ? null : responseBody.getBytes(StandardCharsets.UTF_8);
+            this.responseBody = responseBody == null ? new byte[0] : responseBody.getBytes(StandardCharsets.UTF_8);
         }
 
         public int getStatusCode() {

packages/http-client-java/generator/http-client-generator-test/src/main/java/azure/resourcemanager/multiservicesharedmodels/combined/implementation/CombinedImpl.java

@@ -273,7 +273,7 @@ private static final class HttpResponseImpl extends HttpResponse {
             super(null);
             this.statusCode = statusCode;
             this.httpHeaders = httpHeaders;
-            this.responseBody = responseBody == null ? null : responseBody.getBytes(StandardCharsets.UTF_8);
+            this.responseBody = responseBody == null ? new byte[0] : responseBody.getBytes(StandardCharsets.UTF_8);
         }
 
         public int getStatusCode() {

packages/http-client-java/generator/http-client-generator-test/src/main/java/azure/resourcemanager/nonresource/implementation/NonResourceClientImpl.java

@@ -272,7 +272,7 @@ private static final class HttpResponseImpl extends HttpResponse {
             super(null);
             this.statusCode = statusCode;
             this.httpHeaders = httpHeaders;
-            this.responseBody = responseBody == null ? null : responseBody.getBytes(StandardCharsets.UTF_8);
+            this.responseBody = responseBody == null ? new byte[0] : responseBody.getBytes(StandardCharsets.UTF_8);
         }
 
         public int getStatusCode() {