Fix IllegalStateException

✅ Solution

IllegalStateException in Elasticsearch often arises from concurrent modifications to shared data structures or attempting operations on objects in an invalid state, especially during indexing or serialization. Resolve this by ensuring proper synchronization using locks or concurrent data structures or carefully checking the object's state before performing actions; for serialization issues, verify that all fields are properly initialized and support serialization with the correct version compatibility. Review logs for specific context, such as conflicting document types during merging or race conditions in thread execution, to pinpoint the source of the state transition.