Returns a Boolean value that indicates whether an expression contains no valid data (Null).
Syntax
IsNull(expression)
The required expression argument is a Variant containing a numeric expression or a string expression.
Remarks
IsNull returns True if expression is Null; otherwise, IsNull returns False. If expression consists of more than one variable, Null in any constituent variable causes True to be returned for the entire expression.
The Null value indicates that the Variant contains no valid data. Null is not the same as Empty, which indicates that a variable has not yet been initialized. It's also not the same as a zero-length string (""), which is sometimes referred to as a null string.
Use the IsNull function to determine whether an expression contains a Null value. Expressions that you might expect to evaluate to True under some circumstances, such as If Var = Null and If Var <> Null, are always False. This is because any expression containing a Null is itself Null and therefore False.
Example
This example uses the IsNull function to determine if a variable contains a Null.
Dim MyVar, MyCheck
MyCheck = IsNull(MyVar) ' Returns False.
MyVar = ""
MyCheck = IsNull(MyVar) ' Returns False.
MyVar = Null
MyCheck = IsNull(MyVar) ' Returns True.