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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _filters_pb(self):
 """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. """

        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)