@Override
  public synchronized @NotNull Set<RefClass> getSubClasses() {
    LOG.assertTrue(isInitialized());
    if (myDerivedReferences == null) return EMPTY_CLASS_SET;
    return StreamEx.of(myDerivedReferences).select(RefClass.class).toSet();
  }
@Override
  public synchronized @NotNull Set<RefClass> getSubClasses()