static HighlightInfo.@Nullable Builder checkImplicitClassFileIsValidIdentifier(@NotNull PsiJavaFile file) {
    if (!PsiUtil.isAvailable(JavaFeature.IMPLICIT_CLASSES, file)) return null;
    PsiImplicitClass implicitClass = JavaImplicitClassUtil.getImplicitClassFor(file);
    if (implicitClass == null) return null;
    String name = implicitClass.getQualifiedName();
    if (!PsiNameHelper.getInstance(file.getProject()).isIdentifier(name)) {
      return HighlightInfo.newHighlightInfo(HighlightInfoType.ERROR)
        .range(file)
        .fileLevelAnnotation()
        .description(JavaErrorBundle.message("error.implicit.class.has.invalid.file.name"));
    }
    return null;
  }
static HighlightInfo.@Nullable Builder checkImplicitClassFileIsValidIdentifier(@NotNull PsiJavaFile file)