How to debug a set variable in spoon without error (parent job not available)

I have a transformation that is doing some validation. If the result is true, a row is sent to a set variable step. That step will set a constant field 'TRUE' with the value 'Y' to a variable. If the input is not validated, the step will not receive any rows and instead set default value 'N'.

This works fine in the program, but whenever this individual transformation is debugged in spoon, set variable step crash because:

Can't set variable [VariableName] on parent job: the parent job is not available

Any good solution to this?