When creating a new container, choosing the world option but not picking one causes JS error

[itzg]

TypeError: Cannot read property 'id' of undefined
    at m.$scope.submitNewContainer (new-container-ctrl.js:104)
    at fn (eval at <anonymous> (angular.min.js:226), <anonymous>:4:245)
    at b (angular.min.js:124)
    at e (angular.min.js:268)
    at m.$eval (angular.min.js:142)
    at m.$apply (angular.min.js:143)
    at m.scopePrototype.$apply (chrome-extension://ighdmehidhipcmcojjgiloacoafjmpfk/dist/hint.js:1427)
    at HTMLFormElement.<anonymous> (angular.min.js:268)
    at HTMLFormElement.m.event.dispatch (jquery.min.js:3)
    at HTMLFormElement.r.handle (jquery.min.js:3)