The ASQN attribute has an intrinsic read-only property .IsSqlNull. This may have the values True or False. If the field is SQL Null, .IsSqlNull is True, otherwise it is False.
Note that Intrinsic properties can also be used in conditions that are defined by or passed to an I/O module, but this is not recommended. Refer to Specifying WHERE Parameters in I/O Commands.
Also See
ASQN (Allow SQL Nulls) attribute
Assignment, Conditions, and Expressions with Fields allowing SQL Null
