sails js promises - cannot method then of undefined

I have the following code executing inside a controller in Sailsjs. I get the following error back

TypeError: Cannot call method 'then' of undefined

Why is this error occurring?

        User.query("select id from User where username='" + req.param("userid") + "'").then(function(userData){
        console.log(userData);
        return userData;
    }).fail(function (err) {
        console.log("Handled");
    });