Potential problem with is<T> method: cannot read property 'resultType' of undefined

[brakmic]

Describe the bug
While trying to update the morphir-bosque code I encountered a problem that we've talked about two times already.

It's the error Cannot read property 'resultType' of undefined.

I have ported the original code into a simpler code file:

namespace NSMain;

typedef Price = Int;

entity OrderPrice {

}

entity Limit provides OrderPrice {
    invariant $price >= 0;
    field price: Price;
}

function lockinPrice(requestPrice: OrderPrice, marketPrice: Price): Price {
    return requestPrice.is<Limit>() ? requestPrice.price : marketPrice;
}

entrypoint function main(): Bool {
    let requestPrice = Limit@{price=200};
    let marketPrice: Price = 10;
    return lockinPrice(requestPrice, marketPrice) < ((marketPrice * 9) / 10);
}

The problem has something to do with the is<T> method from the lockinPrice function, if I am not mistaken. And I have also tried various tricks you mentioned in the two other issues. However, the error still persists.

[brakmic]

My bad! It seems that my demo code is getting compiled. The error was that I used "entity" for OrderPrice instead of "concept".
However, the original code still doesn't compile.

So the error is somewhere else. Will close this issue then.