arcade calculation - once() or only when null

[PaulPetersen1]

I've been using Arcade calcuation expressions with good success in Field Maps. However, I'd like to know if it's possible to trigger the calculation only when the associated field is null. This would be similar to the once() operator, of the Survey123 whenEmpty calculation mode. Basically I want to make sure the calculation (the inspection date) doesn't get overwritten if the Smartform is opened at a later time after initial collection.

[KenBuja · Accepted solution]

The IsEmpty function returns "true" if the value is null or empty ('').

If (!IsEmpty($feature.InspectionDate)){
  //save a new Inspection Date
}

[PaulPetersen1]

Thanks, that helps.