    def index(self, vocab: Vocabulary):
        """
        Given a :class:`Vocabulary`, converts all strings in this field into (typically) integers.
        This `modifies` the `Field` object, it does not return anything.

        If your `Field` does not have any strings that need to be converted into indices, you do
        not need to implement this method.
        """
        pass
Given a :class:`Vocabulary`, converts all strings in this field into (typically) integers.
This `modifies` the `Field` object, it does not return anything.

If your `Field` does not have any strings that need to be converted into indices, you do
not need to implement this method.
allennlp/data/fields/field.py