<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _querystring(self):
 """Get additional keyword arguments"""


        kw = {}
        for key in self.KNOWN_QUERY_OPTIONS:
            val = getattr(self, key)
            if val is not None:
                kw[key] = val
        return kw