private static boolean isFileSeparator(PsiExpression argument) {
    if (argument instanceof PsiReferenceExpression ref &&
        "separator".equals(ref.getReferenceName()) &&
        ref.resolve() instanceof PsiField field) {
      PsiClass cls = field.getContainingClass();
      return cls != null && CommonClassNames.JAVA_IO_FILE.equals(cls.getQualifiedName());
    }
    return false;
  }
private static boolean isFileSeparator(PsiExpression argument)