以下代码在运行时， 第一个方法并没有把结果传递到第二个方法， 请问是什么问题？

var Q = require("q");

var getEmailBySessionId = function (mongo_client, redis_client, sid){
        var deferred = Q.defer();
        redis_client.get('s:' + sid, function(err, email) {
                if (!err){
                      deferred.resolve({db : mongo_client, email : email});
                }else{
                      deferred.reject({err_code: -1});
                }
        });
        return deferred.promise;
};

var getUsersCount = function (data) {
        var db = data['db'];
        var deferred = Q.defer();
        db.collection.count({}, {}, function(err, count){
                if (!err){
                        data['count'] = count;
                        deferred.resolve(data);
                }else{
                        deferred.reject({err_code : -2});
                }
        });
        return deferred.promise;
});

getEmailBySessionId(mongo_client, redis_client, sid)
                           .then(getUsersCount)
                           .done(console.log, console.error);