Fix IllegalStateException

✅ Solution

The IllegalStateException in Logstash often arises when a pipeline attempts to access a field or event's state in an invalid context, such as accessing a non-existent field or modifying an event after it has been finalized. Ensure your filters correctly handle null or missing fields using conditionals (if statements) before accessing them and avoid modifying the event after it has been sent to downstream stages like the output. Review configurations for potentially problematic field references or late modifications that could trigger this improper state access.