The validity of the covenant not to sue may be litigated in the action at law. Schofield v. Company, 90 N.H. 31; Dion v. Mills, ante, 414. The construction of the declaratory judgment statute (R. L., c. 370, s. 20) barring its service when other remedy is available and adequate (Gitsis v. Thornton, 91 N.H. 192, and cases cited) therefore required the dismissal of the petition. The reasons assigned for a reversal of the construction or for an exception to it in the case are not sufficiently impressive to invite discussion.