
Null (or nil) is the computer science concept of an undefined or unbound object.
Some languages have an explicit way to access the null object, and some don't.
Some languages distinguish the null object from undefined values, and some don't.



Task

Show how to access null in your language by checking to see if an object is equivalent to the null object.


This task is not about whether a variable is defined. The task is about "null"-like values in various languages, which may or may not be related to the defined-ness of variables in your language.

/*REXX program demonstrates null strings, and also undefined values. */
 
if symbol('ABC')=="VAR" then say 'variable ABC is defined, value='abc"<<<"
                        else say "variable ABC isn't defined."
xyz=47
if symbol('XYZ')=="VAR" then say 'variable XYZ is defined, value='xyz"<<<"
                        else say "variable XYZ isn't defined."
drop xyz
if symbol('XYZ')=="VAR" then say 'variable XYZ is defined, value='xyz"<<<"
                        else say "variable XYZ isn't defined."
cat=''
if symbol('CAT')=="VAR" then say 'variable CAT is defined, value='cat"<<<"
                        else say "variable CAT isn't defined."