Error when trying to create Object Occurences on Model

Hi everyone

I'm trying to create object occurences on a model using the following function : 

function createOcc(model,oObjDef,nType){
    
    var obj = model.createObjOcc(nType,oObjDef,oX,oY,true);
    return obj;
    
}

Before sending the model to this function, I'm storing the model in a variable by using this line of code :

var app2systemCatalog = g_oDatabase.FindGUID("a918c921-1727-11ec-619c-d63b1f542671");

After running my script I get an error on the first line of the "create Occ" function, the error looks like this :

Apparently , my model is "invalid" , I don't understand why.

If someone knows where the problem could be, I'd appreciate some help.

Thank you.