code: def check_token(self):
          
          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
docs: Checks if the token exists
          :return bool: True if it exists on the store