func isEmptyString(n ast.Expr) bool {
	lit, ok := n.(*ast.BasicLit)
	return ok && lit.Kind == token.STRING && len(lit.Value) == 2
}
func isEmptyString(n ast.Expr) bool {
	lit, ok := n.(*ast.BasicLit)
	return ok && lit.Kind == token.STRING && len(lit.Value) == 2
}
// isEmptyString returns true if n is an empty string literal.