@Nullable
  private static Boolean isOverrides(final PyFunction pyFunction) {
    final PyClass clazz = PyUtil.getContainingClassOrSelf(pyFunction);
    assert clazz != null : "Refactoring called on function, not method: " + pyFunction;
    for (final PyClass parentClass : clazz.getSuperClasses(null)) {
      final PyFunction parentMethod = parentClass.findMethodByName(pyFunction.getName(), true, null);
      if (parentMethod != null) {
        return true;
      }
    }
    return null;
  }
@Nullable
  private static Boolean isOverrides(final PyFunction pyFunction)