Deepseek Coder is purpose-built for code-related tasks and excels at tracing runtime errors like null pointer exceptions in Java. You can paste your stack trace and relevant code, and it will walk through the call chain to identify where the null reference originates. It is free to use in the app, making it a low-friction first stop for debugging. Claude Sonnet is a strong alternative when you need deeper contextual reasoning across a larger codebase, and Cursor is worth considering if you want an IDE-integrated experience that lets the tool inspect your code directly in your editor.