[Fix] error in dataset default selection

app.py

@@ -71,7 +71,7 @@ def validate_inputs(selected_models, selected_dataset):
 def update_datasets_based_on_models(selected_models, current_dataset):
     try:
         available_datasets = get_leaderboard_datasets(selected_models) if selected_models else []
-        valid_dataset = current_dataset if current_dataset in available_datasets else "mmlu_pro"
+        valid_dataset = current_dataset if current_dataset in available_datasets else None
         return gr.update(
             choices=available_datasets,
             value=valid_dataset