Update OpenAiChatModel.java

Auto-cherry-pick to 1.0.x
Fixes #3376

Fix NullPointerException caused by empty choice.index() and Map.of() with null value

- Resolve the issue where choice.index() returns an empty value, leading to a NullPointerException.
- Ensure that Map.of() does not accept null values to prevent runtime errors.
- Implement null checks and provide default values to handle edge cases gracefully.
- Update unit tests to cover scenarios where choice.index() is empty or null.

Signed-off-by: yiangjm <[email protected]>

Author: yangjm-41

models/spring-ai-openai/src/main/java/org/springframework/ai/openai/OpenAiChatModel.java

@@ -216,7 +216,7 @@ public ChatResponse internalCall(Prompt prompt, ChatResponse previousChatRespons
 					Map<String, Object> metadata = Map.of(
 							"id", chatCompletion.id() != null ? chatCompletion.id() : "",
 							"role", choice.message().role() != null ? choice.message().role().name() : "",
-							"index", choice.index(),
+							"index", choice.index() != null ? choice.index() : 0,
 							"finishReason", choice.finishReason() != null ? choice.finishReason().name() : "",
 							"refusal", StringUtils.hasText(choice.message().refusal()) ? choice.message().refusal() : "",
 							"annotations", choice.message().annotations() != null ? choice.message().annotations() : List.of(Map.of()));
@@ -315,7 +315,7 @@ public Flux<ChatResponse> internalStream(Prompt prompt, ChatResponse previousCha
 							Map<String, Object> metadata = Map.of(
 									"id", id,
 									"role", roleMap.getOrDefault(id, ""),
-									"index", choice.index(),
+									"index", choice.index() != null ? choice.index() : 0,
 									"finishReason", choice.finishReason() != null ? choice.finishReason().name() : "",
 									"refusal", StringUtils.hasText(choice.message().refusal()) ? choice.message().refusal() : "",
 									"annotations", choice.message().annotations() != null ? choice.message().annotations() : List.of());