Checks if the token exists
        :return bool: True if it exists on the store

def check_token(self):
        """
        Checks if the token exists
        :return bool: True if it exists on the store
        """
        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
        return doc and doc.exists