CALL_NON_FUNCTION_AS_CONSTRUCTOR (native)

I'm trying to use a new schema in my db, but get errors while trying to instantiate it. I have two other schemas (in two different model files in the folder "models"), that works perfect, and they are shaped in the same way. What does the error message mean and what can I do different to prevent it from occur?

I don't thinks its any problem with the other code in the controller, because i've tried to instantiate another db model in the same place using the same syntax, and that works fine.

The error I get: 500 TypeError: object is not a function at Schema.CALL_NON_FUNCTION_AS_CONSTRUCTOR (native)

Sorry for all the code below. I didn't know what I could exclude in this case. Anyway, thanks in advance!

controller file:

module.exports = function(app, service) {
    var imageModel = service.useModel('image');

    app.post('/file-upload', function(req, res, next) {

           // other code...

        var imageAdd = new imageModel.ImgSchema();

    }
}

mongodb model (models/image.js):

module.exports = function (mongoose) {

    var modelObject = {};

    var Schema = mongoose.Schema,
        ObjectId = Schema.ObjectId;

    var ImgSchema = new Schema({
        name : String,
        size : Number,
        type : String
    });

    modelObject.ImgSchema = ImgSchema;
    modelObject.Images = mongoose.model('Images', ImgSchema);

    return modelObject;
};

For mongodb I'm using a service file (service.js):

var environment;
var mongoose = require('mongoose');

module.exports.init = function(env, mongoose) {
    environment = env;
    mongoose = mongoose;
};

module.exports.useModel = function (modelName) {
    var checkConnectionExists = (mongoose.connection.readyState === 1 || mongoose.connection.readyState === 2);
    if(!checkConnectionExists)
        mongoose.connect(environment.db.URL);
    return require("./models/" + modelName)(mongoose);
};

module.exports.useModule = function (moduleName) {
    return require("./modules/" + moduleName);
};