docs: def exists(self):
          """Check if a target exists
  
          This function is called by :mod:`luigi` to check if a task output exists. By default,
          :mod:`luigi` considers a task as complete if all it targets (outputs) exist.
  
          Returns:
              bool: ``True`` if target exists, ``False`` otherwise
          """
          # get DB connection
          session = client.get_client().create_session()
  
          # query for target existence
          ret = self._base_query(session).count() > 0
  
          session.close()
  
          return ret