code: def get_operation_type(self, operation_name):
          # type: (Optional[str]) -> Optional[str]
          
          operations_map = self.operations_map
          if not operation_name and len(operations_map) == 1:
              return next(iter(operations_map.values()))
          return operations_map.get(operation_name)
docs: Returns the operation type ('query', 'mutation', 'subscription' or None)
          for the given operation_name.
          If no operation_name is provided (and only one operation exists) it will return the
          operation type for that operation