refactor: address review comments regarding npe, readme update and copying headers

Author: ewanharris

README.md

@@ -19,6 +19,7 @@ This is an autogenerated Java SDK for OpenFGA. It provides a wrapper around the
 - [Installation](#installation)
 - [Getting Started](#getting-started)
   - [Initializing the API Client](#initializing-the-api-client)
+  - [Custom Headers](#custom-headers)
   - [Get your Store ID](#get-your-store-id)
   - [Calling the API](#calling-the-api)
     - [Stores](#stores)
@@ -294,6 +295,7 @@ public class Example {
                             "X-Custom-Header", "overridden-value" // this will override the default value for this request only
                     )
                 );
+        var response = fgaClient.read(request, options).get();
     }
 }
 ```

src/main/java/dev/openfga/sdk/api/client/OpenFgaClient.java

@@ -248,11 +248,13 @@ public CompletableFuture<ClientReadAuthorizationModelResponse> readAuthorization
             ClientReadAuthorizationModelOptions options) throws FgaInvalidParameterException {
         configuration.assertValid();
         String storeId = configuration.getStoreIdChecked();
-        // Set authorizationModelId from options if available; otherwise, use the default from configuration
-        String authorizationModelId = !isNullOrWhitespace(options.getAuthorizationModelId())
-                ? options.getAuthorizationModelIdChecked()
-                : configuration.getAuthorizationModelId();
-
+        // Set authorizationModelId from options if available; otherwise, require a valid configuration value
+        String authorizationModelId;
+        if (options != null && !isNullOrWhitespace(options.getAuthorizationModelId())) {
+            authorizationModelId = options.getAuthorizationModelIdChecked();
+        } else {
+            authorizationModelId = configuration.getAuthorizationModelIdChecked();
+        }
         var overrides = new ConfigurationOverride().addHeaders(options);
         return call(() -> api.readAuthorizationModel(storeId, authorizationModelId, overrides))
                 .thenApply(ClientReadAuthorizationModelResponse::new);

src/main/java/dev/openfga/sdk/api/configuration/ClientBatchCheckClientOptions.java

@@ -13,6 +13,7 @@
 package dev.openfga.sdk.api.configuration;
 
 import dev.openfga.sdk.api.model.ConsistencyPreference;
+import java.util.HashMap;
 import java.util.Map;
 
 public class ClientBatchCheckClientOptions implements AdditionalHeadersSupplier {
@@ -60,7 +61,7 @@ public ConsistencyPreference getConsistency() {
 
     public ClientCheckOptions asClientCheckOptions() {
         return new ClientCheckOptions()
-                .additionalHeaders(additionalHeaders)
+                .additionalHeaders(additionalHeaders != null ? new HashMap<>(additionalHeaders) : null)
                 .authorizationModelId(authorizationModelId)
                 .consistency(consistency);
     }

src/main/java/dev/openfga/sdk/api/configuration/ClientListRelationsOptions.java

@@ -13,6 +13,7 @@
 package dev.openfga.sdk.api.configuration;
 
 import dev.openfga.sdk.api.model.ConsistencyPreference;
+import java.util.HashMap;
 import java.util.Map;
 
 public class ClientListRelationsOptions implements AdditionalHeadersSupplier {
@@ -61,7 +62,7 @@ public ConsistencyPreference getConsistency() {
     public ClientBatchCheckClientOptions asClientBatchCheckClientOptions() {
         return new ClientBatchCheckClientOptions()
                 .authorizationModelId(authorizationModelId)
-                .additionalHeaders(additionalHeaders)
+                .additionalHeaders(additionalHeaders != null ? new HashMap<>(additionalHeaders) : null)
                 .maxParallelRequests(maxParallelRequests)
                 .consistency(consistency);
     }