def METHOD_NAME(self, xmlns=DEFAULT_XMLNS):
    default_xmlns = DEFAULT_XMLNS
    xmlns_tag = ' xmlns="%s"' % default_xmlns
    source = self.get_xml('original_form').decode('utf-8')
    assert xmlns_tag in source, source
    if xmlns is None:
        source = source.replace(xmlns_tag, '')
    else:
        if xmlns != default_xmlns:
            source = source.replace(default_xmlns, xmlns)
        assert xmlns in source, source
    return source