def func_param_immutable_default_safer(collection=None):
    """
    :param collection: a collection. default None which is immutable and therefor safer.
    :return: collection by appending 'thing'
    """
    if collection is None:
        # safer pattern, instantiate a new mutable object inside the function, not as a parameter default.
        collection = []

    collection.append("thing")
    return collection