def collater(self, samples):
        """
        If we are doing batch sampling, then pick the right collater to use.

        Otherwise we assume all collaters are the same.
        """
        if len(samples) == 0:
            return None
        _, key = self._map_index(samples[0]["full_id"])

        return self.datasets[key].collater(samples)

        If we are doing batch sampling, then pick the right collater to use.

        Otherwise we assume all collaters are the same.
        
decoding/GAD/fairseq/data/multi_corpus_dataset.py