You could mask the problem by turning off errorOnUnhandledRejections, but the error says you're needing to "handle a possible rejection" so you just need to add a catch to your promise.
resource.get().$promise
.then(function (response) {
// do something with the response
}).catch(function (error)) {
// pass the error to the error service
return errorService.handleError(error);
});
Reference: https://github.com/angular-ui/ui-router/issues/2889