kb/java_null_pointer.md

# Java NullPointerException

## Symptoms
- Stacktrace contains `NullPointerException`
- Fails during specific code paths or after deploy
- Sometimes triggered by missing config or feature flags

## Checks
- Inspect stacktrace frames to find source file and line
- Validate configuration/feature flag defaults are present
- Add guards for optional fields and log offending values
- Review recent code changes around the failing area
- Add unit tests covering null/missing data inputs

## Fix
- Add null checks and default values
- Ensure config/flags are loaded before use
- Deploy fix and monitor for recurrence