VB & VBA in a Nutshell: The Language

IsNull Function

Named Arguments

No

Syntax

IsNull(expression)

expression

Use: Required

Data Type: Variant

An expression containing string or numeric data.

Return Value

Boolean (True or False).

Description

Determines whether expression contains any Null data.

Rules at a Glance

• If the expression passed to IsNull contains null data, True is returned; otherwise, IsNull returns False.

• All variables in expression are checked for null data. If null data is found in any one part of the expression, True is returned for the entire expression.

• Although any data type can be passed to the function, only a variant variable can be null. As a result, it makes little sense to pass nonvariant data to the function, since it must always return False.

Programming Tips and Gotchas

• IsNull is useful when returning data from a database. You should check field values in columns that allow Nulls against IsNull before assigning the value to a collection or other variable. This stops the common "Invalid Use of Null" error from occurring.

• IsNull is the only way to evaluate an expression containing a null. For example, the seemingly correct statement:

  If varMyVar = Null Then

  always evaluates to False, even if varMyVar is null. This occurs because the value of an expression containing Null is always Null and therefore False.