src/transformers/trainer.py/Trainer/_load_state_dict_in_model
class Trainer:    def _load_state_dict_in_model(self, state_dict):
        load_result = self.model.load_state_dict(state_dict, strict=False)

        if len(load_result.missing_keys) != 0:
            if self.model._keys_to_ignore_on_save is not None and set(load_result.missing_keys) == set(
                self.model._keys_to_ignore_on_save
            ):
                self.model.tie_weights()
            else:
                logger.warn(f"There were missing keys in the checkpoint model loaded: {load_result.missing_keys}.")
        if len(load_result.unexpected_keys) != 0:
            logger.warn(f"There were unexpected keys in the checkpoint model loaded: {load_result.unexpected_keys}.")