a promise was created in a handler but was not returned from it

[wjzwjh]

In the following code , server pop up warning:a promise was created in a handler but was not returned from it

export function changeTheme(req, res, next) {
var userId = req.user._id;
var theme = String(req.body.theme);
return User.find({
where: {
_id: userId
}
})
.then(user => {
user.theme = theme;
return user.save()
.then(() => {
res.status(204).end();
})
.catch(validationError(res));
});
}

Here is stack Trace:

PUT /api/users/155/theme 200 208.007 ms - 15
Warning: a promise was created in a handler but was not returned from it
at processImmediate as _immediateCallback
From previous event:
at [object Object].Model.findAll (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\sequelize\lib\model.js:1347:18)
at [object Object].Model.findOne (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\sequelize\lib\model.js:1519:34)
at localAuthenticate (passport.js:5:8)
at Strategy._verify (passport.js:35:12)
at Strategy.authenticate (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\passport-local\lib\strategy.js:90:12)
at attempt (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\passport\lib\middleware\authenticate.js:348:16)
at authenticate (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\passport\lib\middleware\authenticate.js:349:7)
at index.js:10:3
at Layer.handle as handle_request
at next (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express\lib\router\route.js:131:13)
at Route.dispatch (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express\lib\router\route.js:112:3)
at Layer.handle as handle_request
at H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express\lib\router\index.js:277:22
at Function.process_params (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express\lib\router\index.js:330:12)
at next (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express\lib\router\index.js:271:10)
at Function.handle (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express\lib\router\index.js:176:3)
at router (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express\lib\router\index.js:46:12)
From previous event:
at Promise.then (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\sequelize\lib\promise.js:21:17)
at E4Store.get (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express-sequelize-session\lib\e4store.js:56:12)
at session (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express-session\index.js:403:11)
at Layer.handle as handle_request
at trim_prefix (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express\lib\router\index.js:312:13)
at H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express\lib\router\index.js:280:7
at Function.process_params (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express\lib\router\index.js:330:12)
at next (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express\lib\router\index.js:271:10)
at initialize (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\passport\lib\middleware\initialize.js:53:5)
at Layer.handle as handle_request
at trim_prefix (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express\lib\router\index.js:312:13)
at H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express\lib\router\index.js:280:7
at Function.process_params (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express\lib\router\index.js:330:12)
at next (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express\lib\router\index.js:271:10)
at cookieParser (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\cookie-parser\index.js:70:5)
at Layer.handle as handle_request
at trim_prefix (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express\lib\router\index.js:312:13)
at H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express\lib\router\index.js:280:7
at Function.process_params (H:\nginx-1.9.14\html\bootswatchMenu2\node_modules\express\lib\router\index.js:330:12)