docs: def from_optional_dicts_by_key(cls, ds: Optional[dict],
                                     force_snake_case=True, force_cast: bool=False, restrict: bool=True) -> TOption[TDict[T]]:
          """From dict of dict to optional dict of instance.
  
          :param ds: Dict of dict
          :param force_snake_case: Keys are transformed to snake case in order to compliant PEP8 if True
          :param force_cast: Cast forcibly if True
          :param restrict: Prohibit extra parameters if True
          :return: Dict of instance
  
          Usage:
  
              >>> from owlmixin.samples import Human
              >>> Human.from_optional_dicts_by_key(None).is_none()
              True
              >>> Human.from_optional_dicts_by_key({}).get()
              {}
          """
          return TOption(cls.from_dicts_by_key(ds,
                                               force_snake_case=force_snake_case,
                                               force_cast=force_cast,
                                               restrict=restrict) if ds is not None else None)