docs: def to_pretty_json(self, ignore_none: bool=True, ignore_empty: bool=False) -> str:
          """From instance to pretty json string
  
          :param ignore_none: Properties which is None are excluded if True
          :param ignore_empty: Properties which is empty are excluded if True
          :return: Json 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_pretty_json())
              {
                  "favorites": [
                      {
                          "name": "Apple",
                          "names_by_lang": {
                              "de": "Apfel",
                              "en": "Apple"
                          }
                      },
                      {
                          "name": "Orange"
                      }
                  ],
                  "id": 1,
                  "name": "Tom"
              }
          """
          return self.to_json(4, ignore_none, ignore_empty)