@NotNull
  default <T extends PyAstElement> T childToPsiNotNull(IElementType elType) {
    final PyAstElement child = childToPsi(elType);
    if (child == null) {
      throw new RuntimeException("child must not be null; expression text " + getText());
    }
    //noinspection unchecked
    return (T)child;
  }
@NotNull
  default <T extends PyAstElement> T childToPsiNotNull(IElementType elType)