docs: def load_meta_data(self, path=None):
          """Load meta data of state model from the file system
  
          The meta data of the state model is loaded from the file system and stored in the meta property of the model.
          Existing meta data is removed. Also the meta data of all state elements (data ports, outcomes,
          etc) are loaded, as those stored in the same file as the meta data of the state.
  
          This is either called on the __init__ of a new state model or if a state model for a container state is created,
          which then calls load_meta_data for all its children.
  
          :param str path: Optional file system path to the meta data file. If not given, the path will be derived from
              the state's path on the filesystem
          :return: if meta data file was loaded True otherwise False
          :rtype: bool
          """
          # TODO: for an Execution state this method is called for each hierarchy level again and again, still?? check it!
          # print("1AbstractState_load_meta_data: ", path, not path)
          if not path:
              path = self.state.file_system_path
          # print("2AbstractState_load_meta_data: ", path)
          if path is None:
              self.meta = Vividict({})
              return False
          path_meta_data = os.path.join(path, storage.FILE_NAME_META_DATA)
  
          # TODO: Should be removed with next minor release
          if not os.path.exists(path_meta_data):
              logger.debug("Because meta data was not found in {0} use backup option {1}"
                           "".format(path_meta_data, os.path.join(path, storage.FILE_NAME_META_DATA_OLD)))
              path_meta_data = os.path.join(path, storage.FILE_NAME_META_DATA_OLD)
              # TODO use the following logger message to debug meta data load process and to avoid maybe repetitive loads
              # if not os.path.exists(path_meta_data):
              #     logger.info("path not found {0}".format(path_meta_data))
  
          try:
              # print("try to load meta data from {0} for state {1}".format(path_meta_data, self.state))
              tmp_meta = storage.load_data_file(path_meta_data)
          except ValueError as e:
              # if no element which is newly generated log a warning
              # if os.path.exists(os.path.dirname(path)):
              #     logger.debug("Because '{1}' meta data of {0} was not loaded properly.".format(self, e))
              if not path.startswith(constants.RAFCON_TEMP_PATH_STORAGE) and not os.path.exists(os.path.dirname(path)):
                  logger.debug("Because '{1}' meta data of {0} was not loaded properly.".format(self, e))
              tmp_meta = {}
  
          # JSON returns a dict, which must be converted to a Vividict
          tmp_meta = Vividict(tmp_meta)
  
          if tmp_meta:
              self._parse_for_element_meta_data(tmp_meta)
              # assign the meta data to the state
              self.meta = tmp_meta
              self.meta_signal.emit(MetaSignalMsg("load_meta_data", "all", True))
              return True
          else:
              # print("nothing to parse", tmp_meta)
              return False