def clean_empty_nodes(xml_str):
    xml = fromstring(xml_str)
    for child in xml.iter():
        for key, value in child.attrib.items():
            if value == '':
                child.attrib.pop(key)
        if not child.attrib and not child.getchildren():
            child.getparent().remove(child)
    return etree.tostring(xml, pretty_print=True, xml_declaration=True, encoding='UTF-8')