code: def _filters_pb(self):
          
          num_filters = len(self._field_filters)
          if num_filters == 0:
              return None
          elif num_filters == 1:
              return _filter_pb(self._field_filters[0])
          else:
              composite_filter = query_pb2.StructuredQuery.CompositeFilter(
                  op=enums.StructuredQuery.CompositeFilter.Operator.AND,
                  filters=[_filter_pb(filter_) for filter_ in self._field_filters],
              )
              return query_pb2.StructuredQuery.Filter(composite_filter=composite_filter)
docs: Convert all the filters into a single generic Filter protobuf.
  
          This may be a lone field filter or unary filter, may be a composite
          filter or may be :data:`None`.
  
          Returns:
              google.cloud.firestore_v1beta1.types.\
              StructuredQuery.Filter: A "generic" filter representing the
              current query's filters.