Ads: "Create New Round" action not working

[ruesato]

When attempting to insert an ad into the forum (Admin > Advanced > Advertisements), I tried to create a new round of ads.

1. Clicked "Create New Round" and a modal appeared prompting me to click "Create"
2. Clicking "Create" resulted in no actions in the UI, but threw the following error:

(anonymous) @ angular.js:13531
sendReq @ angular.js:13257
serverRequest @ angular.js:12998
processQueue @ angular.js:17914
(anonymous) @ angular.js:17962
$digest @ angular.js:19075
$apply @ angular.js:19463
(anonymous) @ angular.js:28819
dispatch @ jquery.js:5087
elemData.handle @ jquery.js:4895
angular.js:15536 TypeError: Cannot read property 'message' of null
    at eval (ad-manager.directive.js:80)
    at processQueue (angular.js:17914)
    at eval (angular.js:17962)
    at Scope.$digest (angular.js:19075)
    at Scope.$apply (angular.js:19463)
    at done (angular.js:13312)
    at completeRequest (angular.js:13569)
    at XMLHttpRequest.requestError (angular.js:13485) "Possibly unhandled rejection: {}"```