def add_node_if_missing(parent_node, child_name):
    child = parent_node.find_descendant(child_name)
    if (not child):
        child = new_child_node(child_name, parent=parent_node)
    return child
def add_node_if_missing(parent_node, child_name):
    child = parent_node.find_descendant(child_name)
    if (not child):
        child = new_child_node(child_name, parent=parent_node)
    return child