coerce null to undefined to work around angular.js #5442

gistfile1.js

'use strict';

angular.module('app')
        .directive('coerceNullToUndefined', function () {
            return {
                restrict: 'A',
                require: 'ngModel',
                link: function (scope, element, attrs, ngModel) {
                    ngModel.$formatters.push(function (value) {
                                if (value === null) {
                                    return undefined;
                                }
                                return value;
                            }
                    );
                }
            };
        });