ISBLANK returns 1 if the value of the specified variable is BLANK (empty) and 0 otherwise. 

SYNTAX:

ISBLANK(Cx)
where :
Cx is a conditional variable x

NOTES:

This function REQUIRES a Cx type variable reference, the Vx variable reference will not work.

EXAMPLES:

V88 = ISBLANK(C71)

In this example, variable 88 will be 1 if variable 71 is empty, and 0 if variable 71 holds a value: