    def collater(self, samples: List[Dict]):
        """
        Generate a mini-batch for this dataset.
        To convert this into a regular mini-batch we use the following
        logic:
            1. Select a dataset using the specified probability distribution.
            2. Call the collater function of the selected dataset.
        """
        if len(samples) == 0:
            return None

        selected_key = self.sampling_func(list(self.datasets.keys()))
        selected_samples = [sample[selected_key] for sample in samples]
        return self.datasets[selected_key].collater(selected_samples)
Generate a mini-batch for this dataset.
To convert this into a regular mini-batch we use the following
logic:
1. Select a dataset using the specified probability distribution.
2. Call the collater function of the selected dataset.
fairseq/data/multi_corpus_sampled_dataset.py