How to use [get-first-value]

The reference page of get-first-value has its arguments, constraints and declaration.

Returns the first non-null value resulting from evaluating its expression, and/or its children nodes.

.data1
   foo1:bar1
   foo2:bar2
.data2:bar3
get-first-value:x:@.data1/*
   get-value:x:@.data2

This node returns only the first non-null value resulting from evaluating its expression, and/or its children nodes. This is useful when you for instance have arguments to some lambda object, but want to apply default values if the argument is not specified - And or want to have guarantees of that only a single value is returned.