如果不存在任何值，如何捕获承诺错误？

Question

当用户输入促销代码时，此促销代码可能存在或不存在。我以这种方式返回错误，但是好像服务器崩溃了，它返回了很多行错误。 如何优化代码使其更简洁？这个表格正确吗？我对节点和JS的控制不多，很难看出哪种方法是最好的...

这是我在控制器中的代码：

var mongoose = require('mongoose'),
    Promotion = mongoose.model('Promotion'),
    q = require('q'),
    Promise = q.Promise;

var PromotionController = {

    applyPromo: function(promoCode) {

    return new Promise(function(resolve, reject) {
            if(promoCode === null) {
                resolve(false);
            }

            Promotion.find({code: promoCode}, function (err, elements) {

                if (err)
                {
                    reject(err);
                }

                if((elements !== null) && (elements.length > 0)) {
                    console.log('OK');
                    console.log(elements[0]);
                    resolve(elements[0]._id);
                }
                else {
                    //reject(new Error('Doesnt exist ' + promoCode));
                }
            });
        });
    }
};

module.exports = PromotionController;

我的服务器显示：

Error: Doesnt exist codeExample
    at /home/user/Documentos/myApi/myServer/api/controllers/promotions.js:36:13
    at /home/user/Documentos/myApi/myServer/node_modules/mongoose/lib/model.js:4599:16
    at /home/user/Documentos/myApi/myServer/node_modules/mongoose/lib/query.js:4122:12
    at cb (/home/user/Documentos/myApi/myServer/node_modules/mongoose/lib/query.js:1777:14)
    at result (/home/user/Documentos/myApi/myServer/node_modules/mongodb/lib/utils.js:414:17)
    at executeCallback (/home/user/Documentos/myApi/myServer/node_modules/mongodb/lib/utils.js:406:9)
    at handleCallback (/home/user/Documentos/myApi/myServer/node_modules/mongodb/lib/utils.js:128:55)
    at cursor.close (/home/user/Documentos/myApi/myServer/node_modules/mongodb/lib/operations/cursor_ops.js:224:62)
    at handleCallback (/home/user/Documentos/myApi/myServer/node_modules/mongodb/lib/utils.js:128:55)
    at completeClose (/home/user/Documentos/myApi/myServer/node_modules/mongodb/lib/cursor.js:893:14)
    at Cursor.close (/home/user/Documentos/myApi/myServer/node_modules/mongodb/lib/cursor.js:912:10)
    at cursor._next (/home/user/Documentos/myApi/myServer/node_modules/mongodb/lib/operations/cursor_ops.js:224:23)
    at handleCallback (/home/user/Documentos/myApi/myServer/node_modules/mongodb-core/lib/cursor.js:204:5)
    at _setCursorNotifiedImpl (/home/user/Documentos/myApi/myServer/node_modules/mongodb-core/lib/cursor.js:433:38)
    at self._endSession (/home/user/Documentos/myApi/myServer/node_modules/mongodb-core/lib/cursor.js:441:46)
    at Cursor._endSession (/home/user/Documentos/myApi/myServer/node_modules/mongodb-core/lib/cursor.js:195:5)
    at Cursor._endSession (/home/user/Documentos/myApi/myServer/node_modules/mongodb/lib/cursor.js:226:59)
    at _setCursorNotifiedImpl (/home/user/Documentos/myApi/myServer/node_modules/mongodb-core/lib/cursor.js:441:17)
    at setCursorNotified (/home/user/Documentos/myApi/myServer/node_modules/mongodb-core/lib/cursor.js:433:3)
    at done (/home/user/Documentos/myApi/myServer/node_modules/mongodb-core/lib/cursor.js:648:16)
    at queryCallback (/home/user/Documentos/myApi/myServer/node_modules/mongodb-core/lib/cursor.js:699:18)
    at /home/user/Documentos/myApi/myServer/node_modules/mongodb-core/lib/connection/pool.js:532:18
    at process._tickCallback (internal/process/next_tick.js:61:11)