<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _list_superclasses(class_def):
 """Return a list of the superclasses of the given class"""

    superclasses = class_def.get('superClasses', [])
    if superclasses:
        # Make sure to duplicate the list
        return list(superclasses)

    sup = class_def.get('superClass', None)
    if sup:
        return [sup]
    else:
        return []