Get request method serializers + default media type.

        Grab serializers from ``method_serializers`` if defined, otherwise
        returns the default serializers. Uses GET serializers for HEAD requests
        if no HEAD serializers were specified.

        The method also determines the default media type.

        :param http_method: HTTP method as a string.
        :returns: Tuple of serializers and default media type.

def get_method_serializers(self, http_method):
        """Get request method serializers + default media type.

        Grab serializers from ``method_serializers`` if defined, otherwise
        returns the default serializers. Uses GET serializers for HEAD requests
        if no HEAD serializers were specified.

        The method also determines the default media type.

        :param http_method: HTTP method as a string.
        :returns: Tuple of serializers and default media type.
        """
        if http_method == 'HEAD' and 'HEAD' not in self.method_serializers:
            http_method = 'GET'

        return (
            self.method_serializers.get(http_method, self.serializers),
            self.default_method_media_type.get(
                http_method, self.default_media_type)
        )