how to check jwt login in node with express

I'm trying to create a login route for my api. The algorithm is as follows:

First check if the user exists in the database(if not, send 404 error). Then I check if the password parameter in the query is the same as in the database(if not, send a 400 error). Finally create a token and send it.

Here is the code:

router.post('/login', function(req, res, next){ 
User.getUserByNick(req.params.nick,function(err, rows){
    if(err){ 
        res.json(err);
    }               
    else if(!f.isEmpty(rows)){
        res.status(404);
        res.json({
            error: 404,
            message: 'Authentication failed. User not found.'
            });
    } 
    else{
        res.json(rows);
        if(res.password != req.params.password){
            res.status(400);
            res.json({
                error: 400,
                message: 'Authentication failed. Wrong password.'
                });
        } 
        else{
            var token = jwt.sign(rows, process.env.JWT_SECRET, {
                    expiresInMinutes: 1440 // expires in 24 hours
            });
            res.json({
                success: true,
                message: 'Enjoy your token!',
                    token: token
                });
            }
        }
    });     
});

But when I try to use the route node crashes. I get the next error in console

/api/node_modules/mysql/lib/protocol/Parser.js:79
    throw err; // Rethrow non-MySQL errors
    ^
ValidationError: "value" must be an object

I don't know why, getUserByNick works nice and it returns [] when the user is not found. Otherwise it sends the json with the rows. So I think it may be when I make rows.password.

via Carlos Manrique Enguita