<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _setdef(argdict, name, defaultvalue):
 """Like dict.setdefault but sets the default value also if None is present. """

    if not name in argdict or argdict[name] is None:
        argdict[name] = defaultvalue
    return argdict[name]