Match serializer by query arg.

def _match_serializers_by_query_arg(self, serializers):
        """Match serializer by query arg."""
        # if the format query argument is present, match the serializer
        arg_name = current_app.config.get('REST_MIMETYPE_QUERY_ARG_NAME')
        if arg_name:
            arg_value = request.args.get(arg_name, None)

            if arg_value is None:
                return None
            # Search for the serializer matching the format
            try:
                return serializers[
                    self.serializers_query_aliases[arg_value]]
            except KeyError:  # either no serializer for this format
                return None

        return None