IsNull

Return TRUE if the expression is NULL, otherwise return FALSE.

Syntax
      IsNull(expression)

Key
   expression    A string or numeric expression.

VBScript makes a distinction between an empty string "" and a NULL value. IsNull() will only detect NULLs.

Examples

Dim boolDemo
boolDemo = IsNull(Me!txtDescription)
If boolDemo = True Then Msgbox "A required value is missing!"

“Art is the elimination of the unnecessary” ~ Pablo Picasso

Related:

Syntax - IsBlank function to detect Empty or NULL or Zero.