Retrieves the token from the store
        :return dict or None: The token if exists, None otherwise

def get_token(self):
        """
        Retrieves the token from the store
        :return dict or None: The token if exists, None otherwise
        """
        token = None
        try:
            doc = self.doc_ref.get()
        except Exception as e:
            log.error('Token (collection: {}, doc_id: {}) '
                      'could not be retrieved from the backend: {}'
                      .format(self.collection, self.doc_id, str(e)))
            doc = None
        if doc and doc.exists:
            token_str = doc.get(self.field_name)
            if token_str:
                token = self.token_constructor(self.serializer.loads(token_str))
        self.token = token
        return token