groovy null safe operator not working

1
votes

Trying to do this:

var = obj?.Prop ?: obj.Prop.toLowerCase()

But I keep getting:

java.lang.NullPointerException: Cannot get property 'Prop' on null object

Isn't this what ? is for? My understanding is obj?.Prop is the same as:

if ( obj != null && obj.Prop ) { .. }

Sometimes obj is null, but if its not I want to set obj.Prop to lower case- cant set toLowerCase() on a null object

2
groovy

2 Answers

3
votes

You'll need to do obj?.Prop?.toLowerCase()

The Elvis operator (?:) is causing obj.Prop.toLowerCase() to be evaluated when the obj?.Prop is null. It's equivalent to writing

var = (obj?.Prop != null) ? obj.Prop : obj.Prop.toLowerCase()
1
votes

The expression following the ?: Is the alternative for the case where the preceding expression is null. If you use the same object in your alternative as you used in the preceding part then you will trigger an npe

Instead do 

obj?.Prop?.toLowerCase()