Fix schema validation in olympiad_bench Doc.specific

[pjavanrood]

Describe the bug

The olympiad_bench task encountered schema validation issues during dataset generation/saving because the specific field in the Doc object was being assigned an empty dictionary {}. This caused a mismatch with the expected Arrow/Parquet schema in some environments.

To Reproduce

task = "olympiad_bench|0"

pipeline = Pipeline(
    tasks=task,
    pipeline_parameters=pipeline_params,
    evaluation_tracker=evaluation_tracker,
    model_config=model_config,
)

pipeline.evaluate()
pipeline.save_and_push_results()
pipeline.show_results()

ArrowNotImplementedError                  Traceback (most recent call last)
Cell In[3], line 37
     29 pipeline = Pipeline(
     30     tasks=task,
     31     pipeline_parameters=pipeline_params,
     32     evaluation_tracker=evaluation_tracker,
     33     model_config=model_config,
     34 )
     36 pipeline.evaluate()
---> 37 pipeline.save_and_push_results()
     38 pipeline.show_results()

File ~/Code/Evalhub/backend/lighteval/src/lighteval/pipeline.py:429, in Pipeline.save_and_push_results(self)
    427 logger.info("--- SAVING AND PUSHING RESULTS ---")
    428 if self.is_main_process():
--> 429     self.evaluation_tracker.save()

File ~/Code/Evalhub/backend/lighteval/src/lighteval/logging/evaluation_tracker.py:273, in EvaluationTracker.save(self)
    270 self.save_results(date_id, results_dict)
    272 if self.should_save_details:
--> 273     self.save_details(date_id, details_datasets)
    275 if self.should_push_to_hub:
    276     self.push_to_hub(
    277         date_id=date_id,
...
File ~/Code/Evalhub/backend/.venv/lib/python3.13/site-packages/pyarrow/error.pxi:155, in pyarrow.lib.pyarrow_internal_check_status()

File ~/Code/Evalhub/backend/.venv/lib/python3.13/site-packages/pyarrow/error.pxi:92, in pyarrow.lib.check_status()

ArrowNotImplementedError: Cannot write struct type 'specific' with no child field to Parquet. Consider adding a dummy child field.

Expected behavior

The specific field should be None (or not passed) when no additional metadata is provided, ensuring compatibility with the expected schema.

Version info

• OS: mac
• Lighteval version: main (local development)