When, in an action for commissions earned by a broker under an oral contract of employment to procure a purchaser of real estate, no illegality in the contract appeared on the face of the complaint or in the evidence to sustain the action, the defense that under the penal code a written authorization to procure a purchaser of real estate is necessary must to be available be specially pleaded. Strunski v. Geiger, 101 N. Y. S. 786, 52 Misc. 134. Compare Jamison v. Hyde, 141 Cal. 109, 74 P. 695. Sec. 668.