<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def make(cls, vol):
 """ Convert uuid to Volume, if necessary. """

        if isinstance(vol, cls):
            return vol
        elif vol is None:
            return None
        else:
            return cls(vol, None)