GetFieldValue has:
 public class GetFieldValue extends VDLFunction {
 [...]
   public static final Arg PA_VAR1 = new Arg.Positional("var");
and also inherits from VDLFunction:
   public static final Arg PA_VAR = new Arg.Positional("var");
>From the name, it looks like PA_VAR1 was deliberately made to not be 
PA_VAR but I don't really understand why.
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