### What problem does this PR solve?

When knowledgebase/dataset created by API, graphrag and raptor can be
null, and will trigger NoneType error when reach to this code, causing
chunking task not able to finish.

![image](https://github.com/user-attachments/assets/998a63e9-611b-4301-8808-24839a05be8a)

Proposed solution will result in None and pass the condition check
without error.

![image](https://github.com/user-attachments/assets/184374fb-e06a-46e6-b8ac-d66a3fd93b59)


### Type of change

-  ✅ Bug Fix (non-breaking change which fixes an issue)