I have a complex Drools (8.33) DMN. I enrich an Object (datatype: MyType) with add. fields with 'context put' => a function call with MyType fails

Question

I have an input as list of Datatype 'MyType' with some string fields (defined as itemComponent).

MyType: {"partner": "xyz", "start": "2020-01-01", ...} A DMN sort() tries to sort the list. After that, I add an info object to each object of MyType.

context put(myObject, {"position": 1, "name": "x"})

Now, I try to call function (BKF) with parameter MyType, giving the result of 'context put'. If the function tries to access a field like:

Literal Expression: if myObject.partner="X" then true else false

the call fails. The call is done inside of another sort() function and I get the error message:

FEEL Error: ...The parameter 'list', in function sort(), raised an exception while sorting by natural order.

Is the Object of MyType not a MyType after using the result of 'context put'?

And is it possible to get a specific error message inside a Drools DMN sort() function?

I removed the access to the field, then the sort() function ran without error. I tried to access the field with 'get value(myObject, "partner") -> didn't work