The Null Data type has only one value NULL, and it is used to represent the absence of a value. There is nothing that can be done with NULL except to check if a value is NULL. The IF statement considers NULL to be false, so one can very quickly test to determine if a variable is NULL or not.
For example, to present a personalized message to a user, the following Airscript Expression will display "Hello {{name}}" to the user if the name variable is not NULL, and it will display "Hello!" if the name variable is NULL (meaning the name is unknown).
IF(name, "Hello {{name}}", "Hello!")