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 (https://github.com/spring-projects/spring-ai/issues/2417) Fixes GH-2423 (https://github.com/spring-projects/spring-ai/issues/2423) Signed-off-by: Wenhao Ma <296232679@qq.com>