docs: def map_query_string(self):
          """Maps the GET query string params the the query_key_mapper dict and
          updates the request's GET QueryDict with the mapped keys.
          """
          if (not self.query_key_mapper or
              self.request.method == 'POST'):
              # Nothing to map, don't do anything.
              # return self.request.POST
              return {}
  
          keys = list(self.query_key_mapper.keys())
  
          return {self.query_key_mapper.get(k) if k in keys else k: v.strip()
                  for k, v in self.request.GET.items()}