Angular/Jasmine: adding .error to callback seems to break unit tests

I encountered an error that occurs only when I have the .error part of my http callback defined. Here is the relevant part of the controller I'm testing:

    vm.dirtyTestGraph = function() {
        vm.graphTitle = 'Deposit Amount';

        $timeout(function(){
            ChartService.get( {index: 'transaction', 'type': 'deposit', period: 'week'} )
            .success(function(res){
              vm.graphLoading = false;
              vm.chartData = res.data;
            }).error(function(err){ //<- HERE
              console.log(err);
            });
        }, 2000);

And the unit test to cover it:

describe('Unit: HomeCtrl', function() {
    var ctrl, scope, $timeout, $httpBackend, Chart, ChartService,uuid4;

    beforeEach(module('dashboardApp'));
    beforeEach(inject(function($controller, $rootScope,_$httpBackend_, _Chart_,
            _$timeout_,_ChartService_,_uuid4_) {
        scope = $rootScope.$new();
        $timeout = _$timeout_;
        Chart = _Chart_;
        ChartService = _ChartService_;
        $httpBackend = _$httpBackend_;
        uuid4 = _uuid4_;
        spyOn(uuid4,'generate').and.returnValue("1");


        spyOn(ChartService, 'get').and.callFake(function() {
            return {
                success: function(callback) { callback( {error:0, data:[{count:'101', time:1416960000000}]} ); },
                error: function(err) { err( {error:1 }); }
            };
        });

        ctrl = $controller('HomeCtrl as vm', {
            $scope: scope,
            Chart: _Chart_,
            ChartService:_ChartService_
        });
    }));
    it('test graph loading async', function() {
        scope.vm.dirtyTestGraph();
        $timeout.flush();
        scope.$digest();
        expect(scope.vm.chartData).toEqual([{count:'101', time:1416960000000}]);
        expect(scope.vm.graphLoading).toBe(false);
    });
});

my unit test fails with:

TypeError: 'undefined' is not an object (near '...}).error(function(err)...')

However if I uncomment the .error() part of my ChartService.get()...

The test passes, why? How can I change my test so I can leave both the .success and .error in my controller?