In Johnston v. Dahlgren, 166 N.Y. 354 (1901), the issue was whether the court could order two plumbers to return a payment made to them for work done on the ground that the plumbers had not properly complied with the state's registration requirements. The court allowed the plumbers to keep the payment, stating: The plumbers had performed their work and the defendant had had the benefit of it. If the latter chose to pay for it, the payment could not be revoked. He might have contested the demand for payment of the plumbing work by reason of the illegality of the contract for its performance; but he did not do so and, therefore, the court will leave the parties as they are. (Id. At 360.)