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

Empty tool call id and name strings causing improper ToolCall 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.

Fixes GH-2417 (#2417)
Fixes GH-2423 (#2423)

Signed-off-by: Wenhao Ma <296232679@qq.com>

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(currentToolCall.id())) {
 				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);
@@ -143,7 +144,7 @@ private ChatCompletionFunction merge(ChatCompletionFunction previous, ChatComple
 		if (previous == null) {
 			return current;
 		}
-		String name = (current.name() != null ? current.name() : previous.name());
+		String name = (StringUtils.hasText(current.name()) ? current.name() : previous.name());
 		StringBuilder arguments = new StringBuilder();
 		if (previous.arguments() != null) {
 			arguments.append(previous.arguments());