examples/flax/language-modeling/run_mlm_flax.py/FlaxDataCollatorForLanguageModeling/__post_init__
class FlaxDataCollatorForLanguageModeling:    def __post_init__(self):
        if 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."
            )