New dot function .ISNULL(var) for use with ordered maps to test for the .NULL condition.
Example:
A$ = $MYMAP(KEY$)
IF A$ = .NULL THEN ? "No such key in map" ! old method (deprecated now)
IF .ISNULL(A$) THEN ? "No such key in map" ! new method
In this example, both methods of checking for .NULL are equivalent, provided that the map contains only string elements and A$ is a string. The .ISNULL(var) method is now preferred though, as it works for non-string elements also.
