Worked on stabilizing AI message processing within the langchain4j/langchain4j repository by addressing a critical bug in the MistralAiChatMessage component. Introduced a robust null-guard for the getContent() method to prevent NullPointerExceptions when handling tool-call scenarios, particularly for OpenAI-compatible payloads that may return null content. Enhanced reliability by developing targeted unit tests using Java and backend development practices, covering tool-calls-only, mixed-content, and text-only message flows. Maintained full API compatibility and ensured code quality with Spotless formatting. The changes focused on reducing production risk and improving the stability of AI-assisted workflows, validated by comprehensive continuous integration results.