def get_duplicate_items_in_list(items):
    """Find duplicate entries in a list.

    :param list items: list of items with possible duplicates.

    :return: the items that occur more than once in input list. Each duplicated
        item will be mentioned only once in the returned list.

    :rtype: list
    """
    seen = set()
    duplicates = set()
    if items:
        for item in items:
            if item in seen:
                duplicates.add(item)
            else:
                seen.add(item)
    return list(duplicates)