docs: def to_yaml(self, ignore_none: bool=True, ignore_empty: bool=False) -> str:
          """From instance to yaml string
  
          :param ignore_none: Properties which is None are excluded if True
          :param ignore_empty: Properties which is empty are excluded if True
          :return: Yaml string
  
          Usage:
  
              >>> from owlmixin.samples import Human
              >>> human = Human.from_dict({
              ...     "id": 1,
              ...     "name": "Tom",
              ...     "favorites": [
              ...         {"name": "Apple", "names_by_lang": {"en": "Apple", "de": "Apfel"}},
              ...         {"name": "Orange"}
              ...     ]
              ... })
              >>> print(human.to_yaml())
              favorites:
                - name: Apple
                  names_by_lang:
                    de: Apfel
                    en: Apple
                - name: Orange
              id: 1
              name: Tom
              <BLANKLINE>
          """
          return util.dump_yaml(traverse(self, ignore_none, force_value=True, ignore_empty=ignore_empty))