code: public ObservableList loadObservableList(
        String breadcrumb,
        ObservableList defaultObservableList
    ) {
      String json = getSerializedPreferencesValue(breadcrumb, gson.toJson(defaultObservableList));
      return FXCollections.observableArrayList(gson.fromJson(json, ArrayList.class));
    }
docs: Searches in the preferences after a serialized ArrayList using the given key,
  deserializes and returns it as ObservableArrayList.
  When an ObservableList is deserialzed, Gson returns an ArrayList
  and needs to be wrapped into an ObservableArrayList. This is only needed for loading.
  
  @param breadcrumb            the key which is used to search the serialized ArrayList
  @param defaultObservableList the default ObservableList
  which will be returned if nothing is found
  @return the deserialized ObservableList or the default ObservableList if nothing is found