@NotNull
  @Override
  public Stream<? extends PsiElement> extractExternalFileImplicitReferences(@NotNull PsiFile psiFile) {
    return Arrays
      .stream(((PsiClassOwner)psiFile).getClasses())
      .flatMap(c -> Arrays.stream(c.getSuperTypes()))
      .map(PsiClassType::resolve)
      .filter(Objects::nonNull);
  }
@NotNull
  @Override
  public Stream<? extends PsiElement> extractExternalFileImplicitReferences(@NotNull PsiFile psiFile)