Better error message when inputs are empty

Author: sgugger

src/transformers/trainer.py

@@ -1934,6 +1934,11 @@ def _prepare_inputs(self, inputs: Dict[str, Union[torch.Tensor, Any]]) -> Dict[s
         handling potential state.
         """
         inputs = self._prepare_input(inputs)
+        if len(inputs) == 0:
+            raise ValueError(
+                "The batch received was empty, your model won't be able to train on it. Double-check that your "
+                f"training dataset contains keys expected by the model: {','.join(self._signature_columns)}."
+            )
         if self.args.past_index >= 0 and self._past is not None:
             inputs["mems"] = self._past