# IsNull Function

Updated: August 2009

Returns a Boolean value that indicates whether an expression contains no valid data (Null).

```
IsNull(expression)
```

## Remarks

The expression argument can be any expression.

IsNull returns True if expression is Null, that is, it contains no valid data; otherwise, IsNull returns False.

The Null value indicates that the variable contains no valid data. Null is not the same as Empty, which indicates that a variable has not yet been initialized. It is also not the same as a zero-length string (""), which is sometimes referred to as a null string.

## Example

The following example illustrates the use of the IsNull function.

```'Dim MyVar, Result

' IsNull returns False.
Result = IsNull(MyVar)

' IsNull returns True.
MyVar = Null
Result = IsNull(MyVar)

' IsNull returns False
MyVar = Empty
Result = IsNull(MyVar)
```

If the expression consists of more than one variable, Null in any constituent variable causes True to be returned for the entire expression.

```' IsNull returns True.
MyVar = Null + 4
Result = IsNull(MyVar)
```

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 that contains a Null is itself Null, and therefore False.

```' This returns False, because an expression
' that contains Null is itself Null.
MyVar = Null
If MyVar = Null Then
Result = True
Else
Result = False
End If
```

Date

History

Reason

August 2009