undefined vs not set in computed_by

[cbelsole]

15:TotalDebt number[2] computed_by { 
  return if(QualifyingMonthlyPitia != undefined, QualifyingMonthlyPitia, 0) + 
         if(OtherMonthlyDebts != undefined, OtherMonthlyDebts, 0) 
}

This returns undefined if the value was never originally set. Once the value is set to undefined the != undefined check works as expected.

[alexandrinaw]

I wasn't able to reproduce this :/ maybe we can come up with a test that demonstrates this