src/transformers/data/data_collator.py/DataCollatorForLanguageModeling/__post_init__
class DataCollatorForLanguageModeling:    def __post_init__(self):
        if self.mlm and self.tokenizer.mask_token is None:
            raise ValueError(
                "This tokenizer does not have a mask token which is necessary for masked language modeling. "
                "You should pass `mlm=False` to train on causal language modeling instead."
            )
        if self.tf_experimental_compile:
            import tensorflow as tf

            self.tf_mask_tokens = tf.function(self.tf_mask_tokens, jit_compile=True)