<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _clean_record(self, record):
 """Remove all fields with `None` values"""

        for k, v in dict(record).items():
            if isinstance(v, dict):
                v = self._clean_record(v)
            if v is None:
                record.pop(k)
        return record