(d) Makena insures his vehicle comprehensively. In the application form, which is incorporated into the policy, Makena undertakes and warrants to keep the vehicle locked at all times and to keep the keys locked in a safe overnight. One night the locked vehicle is damaged by fire. It appears, though, that the vehicle's keys were not locked in a safe at the time and the insurer refuses Makena's claim on the basis of his breach of warranty. Comment on the validity of Makena's claim and of the insurer's defence