adapter.json: improve LangStringSet json serialization

Since `LangStringSet` was changed to be an own class in
a1aaec3, we can check for a
`LangStringSet` via `isinstance()` now and simplify the JSON
serialization.

basyx/aas/adapter/json/json_serialization.py

@@ -77,6 +77,7 @@ def default(self, obj: object) -> object:
  model.Extension: self._extension_to_json,
  model.File: self._file_to_json,
  model.Key: self._key_to_json,
+ model.LangStringSet: self._lang_string_set_to_json,
  model.MultiLanguageProperty: self._multi_language_property_to_json,
  model.Operation: self._operation_to_json,
  model.OperationVariable: self._operation_variable_to_json,
@@ -123,11 +124,11 @@ def _abstract_classes_to_json(cls, obj: object) -> Dict[str, object]:
  if obj.id_short:
  data['idShort'] = obj.id_short
  if obj.display_name:
- data['displayName'] = cls._lang_string_set_to_json(obj.display_name)
+ data['displayName'] = obj.display_name
  if obj.category:
  data['category'] = obj.category
  if obj.description:
- data['description'] = cls._lang_string_set_to_json(obj.description)
+ data['description'] = obj.description
  try:
  ref_type = next(iter(t for t in inspect.getmro(type(obj)) if t in model.KEY_TYPES_CLASSES))
  except StopIteration as e:
@@ -341,14 +342,14 @@ def _data_specification_iec61360_to_json(
  """
  data_spec: Dict[str, object] = {
  'modelType': 'DataSpecificationIEC61360',
- 'preferredName': cls._lang_string_set_to_json(obj.preferred_name)
+ 'preferredName': obj.preferred_name
  }
  if obj.data_type is not None:
  data_spec['dataType'] = _generic.IEC61360_DATA_TYPES[obj.data_type]
  if obj.definition is not None:
- data_spec['definition'] = cls._lang_string_set_to_json(obj.definition)
+ data_spec['definition'] = obj.definition
  if obj.short_name is not None:
- data_spec['shortName'] = cls._lang_string_set_to_json(obj.short_name)
+ data_spec['shortName'] = obj.short_name
  if obj.unit is not None:
  data_spec['unit'] = obj.unit
  if obj.unit_id is not None:
@@ -379,7 +380,7 @@ def _data_specification_physical_unit_to_json(
  'modelType': 'DataSpecificationPhysicalUnit',
  'unitName': obj.unit_name,
  'unitSymbol': obj.unit_symbol,
- 'definition': cls._lang_string_set_to_json(obj.definition)
+ 'definition': obj.definition
  }
  if obj.si_notation is not None:
  data_spec['siNotation'] = obj.si_notation
@@ -474,7 +475,7 @@ def _multi_language_property_to_json(cls, obj: model.MultiLanguageProperty) -> D
  """
  data = cls._abstract_classes_to_json(obj)
  if obj.value:
- data['value'] = cls._lang_string_set_to_json(obj.value)
+ data['value'] = obj.value
  if obj.value_id:
  data['valueId'] = obj.value_id
  return data