fix llamaindex CompletionResponse serialize error

[nightosong]

While I use langfuse with llamaindex, I get an error output:

received error response: {'message': 'Invalid request data', 'errors': ['Expected object, received string']}
Received 400 error by Langfuse server, not retrying: {'message': 'Invalid request data', 'errors': ['Expected object, received string']}

Then I debug the task_manager file and find this code data = json.dumps(kwargs, cls=EventSerializer) .
In my case, the output object in body is type of <class 'llama_index.core.base.llms.types.CompletionResponse'>.
When it executes this line of default() in EventSerializer, a TypeError will be thrown.
TypeError: 'MockValSer' object cannot be converted to 'SchemaSerializer' (pydantic 2.8.2)

if isinstance(obj, BaseModel):
    return obj.dict()

---

I just realized that this issue is caused by the type from llamaindex.
Would there be any risks if I handle all of the CompletionResponse here?

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[greptile-apps]

Disclaimer: Experimental PR review

PR Summary

This pull request addresses a serialization issue with LlamaIndex's CompletionResponse object in the EventSerializer class, resolving an 'Invalid request data' error when using langfuse with llamaindex.

• Modified EventSerializer.default() in langfuse/serializer.py to handle CompletionResponse objects by converting them to strings
• Added "CompletionResponse" to the condition checking for LlamaIndex objects that require special handling
• This change ensures proper serialization of CompletionResponse objects, preventing TypeError exceptions
• The fix maintains consistency with how StreamingResponse objects are already handled in the serializer
• Users working with LlamaIndex and langfuse should no longer encounter the 'Invalid request data' error related to CompletionResponse serialization

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[greptile-apps]

Disclaimer: Experimental PR review

PR Summary

This pull request addresses a serialization issue with LlamaIndex's CompletionResponse object in the EventSerializer class of the langfuse-python library.

• Modified EventSerializer.default() to handle CompletionResponse objects by converting them to strings
• The fix resolves the 'Invalid request data' error when using langfuse with llamaindex
• While effective, this solution may not be optimal long-term as it loses the structured data of CompletionResponse objects
• Consider exploring a more robust serialization method that preserves CompletionResponse structure in future updates
• Recommend adding tests in /tests/test_llama_index.py to verify the serialization of CompletionResponse objects

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