<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_highlight(self):
 """ Remove the empty highlight """

        if not self.valid:
            return

        for hit in self._results['hits']['hits']:
            if 'highlight' in hit:
                hl = hit['highlight']
                for key, item in list(hl.items()):
                    if not item:
                        del hl[key]