@staticmethod
def _list_union(list_1, list_2):
    """Union of list that aren't hashable

        Can't use here set union because the items in the lists are
        dictionaries and they are not hashable for set.

        :return: list - union list
        """
    for target_item in list_2:
        if target_item not in list_1:
            list_1.append(target_item)
    return list_1
