Spring-ai fix #625： No serializer found for class org.springframework.ai.openai.metadata.OpenAiImageResponseMetadata

The reason is that the OpenAiImageResponseMetadata class does not have standard getter methods.

Comment From: izeye

https://github.com/spring-projects/spring-ai/issues/625 that this PR tries to resolve seems to have been resolved already via ac518df4db9187a92793de8a81db4115502d3a76.

Comment From: markpollack

Yes, this code has already been updated in main. Thanks in anycase!!