private static PsiField getIfOneStaticSelfInstance(PsiClass aClass) {
    Stream<PsiField> fieldStream = Arrays.stream(aClass.getFields());

    StreamEx<PsiField> enclosingClassFields =
      StreamEx.iterate(aClass.getContainingClass(), nonNull(), c -> c.getContainingClass()).filter(nonNull())
              .flatMap(c -> Stream.of(c.getFields()));
    fieldStream = Stream.concat(fieldStream, enclosingClassFields);

    fieldStream = Stream.concat(fieldStream,
                                Arrays.stream(aClass.getInnerClasses())
                                      .filter(innerClass -> innerClass.hasModifierProperty(PsiModifier.STATIC))
                                      .flatMap(innerClass -> Arrays.stream(innerClass.getFields())));

    final List<PsiField> fields = fieldStream.filter(field -> resolveToSingletonField(aClass, field)).limit(2).toList();
    return fields.size() == 1 ? fields.get(0) : null;
  }
private static PsiField getIfOneStaticSelfInstance(PsiClass aClass)