How to pass operator's output in .expand() in airflow 2.5

Question

I am currently working with an operator that returns a continuation token. Considering that the operator is called FrOperator and I have a sensor that will take this operator's continuation token FrSensor.

Airflow doesn't seem to be passing the output when providing the `

expanded_froperator = FrOperator.partial(<FIXED_VALUES>).expand(<SOMETHING>)
expanded_frsensor = FrSensor.partial(<FIXED_VALUES>).expand(expanded_froperator.output)

Any idea what am I doing wrong?

expanded_froperator.output seems to be returning a None value in Xcoms causing the dag to be skipped.