code: def find_filter(self, filter_cls):
          
          for filter_instance in self.filters:
              if isinstance(filter_instance, filter_cls):
                  return filter_instance
  
          return None
docs: Find or create a filter instance of the provided ``filter_cls``. If it
          is found, use remaining arguments to augment the filter otherwise
          create a new instance of the desired type and add it to the
          current :class:`~es_fluent.builder.QueryBuilder` accordingly.