Angular UI Router Nullable Date

app.config(['$urlMatcherFactoryProvider', function ($urlMatcherFactoryProvider) {
        $urlMatcherFactoryProvider.defaultSquashPolicy(true);

        $urlMatcherFactoryProvider.type('nullableDate', {
            encode: function (val) {
                if (ng.isUndefined(val) || !ng.isDate(val) || val == null) return;

                return [
                    val.getFullYear(),
                    ('0' + (val.getMonth() + 1)).slice(-2),
                    ('0' + val.getDate()).slice(-2)
                ].join("-");
            },
            decode: function (val) {
                if (ng.isUndefined(val) || !ng.isDate(val) || val == null) return;

                return new Date(val);
            },
            is: function(val) {
                 return val instanceof Date && !isNaN(val.valueOf());
            },
            equals: function (a, b) {
                if (ng.isUndefined(a) || !ng.isDate(a) || a == null) return false;
                if (ng.isUndefined(b) || !ng.isDate(b) || b == null) return false;

                return a.toISOString() === b.toISOString();
            },
            pattern: /[0-9]{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[1-2][0-9]|3[0-1])/
        });
    }]);