code: def expected(self, dynamizer):
          
          if self._expect_kwargs:
              return encode_query_kwargs(dynamizer, self._expect_kwargs)
          if self._expected is not NO_ARG:
              ret = {}
              if is_null(self._expected):
                  ret['Exists'] = False
              else:
                  ret['Value'] = dynamizer.encode(self._expected)
                  ret['Exists'] = True
              return {self.key: ret}
          return {}
docs: Get the expected values for the update