fix(openai): prevent incorrect ToolCall merging caused by empty id strings

Empty tool call id strings causing improper TooCall merging during OpenAI stream processing, resulting in incorrect function calling responses. This fix ensures both null and empty strings are properly validated before merging operations.

Relates gh-2417,gh-2423

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

Author: yangtuooc

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

@@ -31,6 +31,7 @@
 import org.springframework.ai.openai.api.OpenAiApi.LogProbs;
 import org.springframework.ai.openai.api.OpenAiApi.Usage;
 import org.springframework.util.CollectionUtils;
+import org.springframework.util.StringUtils;
 
 /**
  * Helper class to support Streaming function calling.
@@ -111,7 +112,7 @@ private ChatCompletionMessage merge(ChatCompletionMessage previous, ChatCompleti
 				throw new IllegalStateException("Currently only one tool call is supported per message!");
 			}
 			var currentToolCall = current.toolCalls().iterator().next();
-			if (currentToolCall.id() != null) {
+			if (StringUtils.hasText(toolCallId)) {
 				if (lastPreviousTooCall != null) {
 					toolCalls.add(lastPreviousTooCall);
 				}
@@ -133,7 +134,7 @@ private ToolCall merge(ToolCall previous, ToolCall current) {
 		if (previous == null) {
 			return current;
 		}
-		String id = (current.id() != null ? current.id() : previous.id());
+		String id = (StringUtils.hasText(current.id()) ? current.id() : previous.id());
 		String type = (current.type() != null ? current.type() : previous.type());
 		ChatCompletionFunction function = merge(previous.function(), current.function());
 		return new ToolCall(id, type, function);