AngularJS和Sharepoint与工厂，产生一个空值

Question

当我运行此代码并且只想获取列表中的所有项目时，控制台会告诉我“无法读取null的属性'readOrganizations'。这是我第一次使用工厂，所以请帮忙！

代码如下：

app.factory("organizationsService", ["$rootScope", function($rootScope) {
    var svc = {};
    var data = null;

    var siteURL = "dthswdththrth";
    
    //CRUD
    svc.createOrganization = function(organization) {
        //REST call to POST data for SP
        data.push(organization);
    }

    svc.readOrganizations = function() {
        $http({
            method: 'GET',
            url: siteURL + '/_api/web/Lists/getbytitle(\'Organizations\')/Items',
            headers: {
                'Accept': 'application/json; odata=verbose'
            }
        }).success(function(d) {
            $(d.d.results).each(function(i, e) {
                data.push({
                    id: e['Id'],
                    title: e['Title']
                });
            });
            callback(data);
        }).error(function(er) {
            alert(er);
        });
    }

    svc.updateOrganization = function(index, organization) {
        //REST call to MERGE data for SP
        data[index] = organization;
    }

    svc.deleteOrganization = function(index) {
        //REST call to DELETE data for SP
    }

    return data;
}]);

app.controller("organizationsController", ["$scope", "$location", "$routeParams", "organizationsService",
    function($scope, $location, $routeParams, organizationsService) {
        $scope.data = organizationsService.readOrganizations();

        $scope.addOrganization = function() {
            $location.path("/organizations/add");
        };

        $scope.editOrganization = function(index) {
            $location.path("/organizations/" + index);
        };
    }
]);

工厂/服务是否完全必要？感谢您的帮助！