def METHOD_NAME(elem):
    """
    Changes value of empty XML tags to empty string.
    This changes lxml behavior to render these tags as
    <tag></tag> instead of <tag />
    """
    elements = [elem]
    while elements:
        elem = elements.pop()
        if elem.tag is etree.Entity:
            continue
        if elem.text is None:
            elem.text = ""
        elements.extend(elem)