private static @Nullable Filter<PsiClass> createFilter(final @Nullable ClassFilter classFilter) {
    if (classFilter == null) {
      return null;
    }
    else {
      return new Filter<>() {
        @Override
        public boolean isAccepted(final PsiClass element) {
          return ReadAction.compute(() -> DumbService.getInstance(element.getProject()).isDumb() || classFilter.isAccepted(element));
        }
      };
    }
  }
private static @Nullable Filter<PsiClass> createFilter(final @Nullable ClassFilter classFilter)