A simple and quick way to check if a property within nested objects and/or collections exist is to check if the expression is Null or not.

For example with the following expression:
$myObject.Prop1.Prop2.Prop3

The existance of Prop3 can be confirmed with the following:

If($myObject.Prop1.Prop2.Prop3#Null) // Property Exists Else // Property Does Not Exist End if

A caveat of this implementation is that each of the items in the expression must either be a collection, object, or nonexistant. Because the expression uses dot notation, if one of the parts of the expression evaluates to something else like a Text then a syntax error # -10716 will get triggered complaining that an object or collection was expected.

For example the following will trigger the error:

$myObject:=New object("Prop1";"Hello") If($myObject.Prop1.Prop2.Prop3#Null)