how to resolve sorting error of mongoose?

I am getting this error while sorting through mongoose : TypeError: Invalid sort value: {field: submittedDate } My Code part is:

var image = mongoose.model('Image');
var allImages =  image.find({reviewed:true },null,{sort:{"submittedDate":-1}}, function (err, images)
    {
        if(err)
        {
            logger.info("Error occured");
            throw err;
        }
        else
        {
            logger.info("images sorted are:",images);
            cb(images);
        }

    });

any help will be appriciated.

I resolved my problem by sorting in this way:

image.find({reviewed:true },{limit:10},{sort:{"submittedDate":-1}}, function (err, images){
}