<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def register_related(cls, related_name):
 """ Register a related item that should be cloned when this model is. :param related_name: Use the name you would use in filtering i.e.: book not book_set. """


        if not hasattr(cls, '_clone_related'):
            cls._clone_related = []

        if type(cls._clone_related) != type([]):
            cls._clone_related = list(cls._clone_related)

        if not related_name in cls._clone_related:
            cls._clone_related.append(related_name)