ACC: "Invalid Use of Null" or "#Error" Err in Custom Function

SYMPTOMS

Moderate: Requires basic macro, coding, and interoperability skills.

A user-defined function may return either of these error messages: "Invalid Use of Null!" or "#Error."

CAUSE

If a field's data type is explicitly defined as any type other than Variant, Microsoft Access is unable to compare the variable to Null.

RESOLUTION

Define the variable as Variant, which includes the Date/Time, Floating- point Number, and String data types.

MORE INFORMATION

This article assumes that you are familiar with Visual Basic for Applications and with creating Microsoft Access applications using the programming tools provided with Microsoft Access. For more information about Visual Basic for Applications, please refer to your version of the "Building Applications with Microsoft Access" manual.

NOTE: Visual Basic for Applications is called Access Basic in Microsoft Access versions 1.x and 2.0. For more information about Access Basic, please refer to the "Introduction to Programming" manual in Microsoft Access version 1.x or the "Building Applications" manual in Microsoft Access version 2.0

If the following function is used to evaluate a field that may return a Null value, the function will return the error "Invalid Use of Null!" or "#Error" if the field is null:

   Function IsFieldNull (MyValue As String)
      If IsNull(MyValue) Then
         IsFieldNull = "The field is null!"
      Else
         IsFieldNull = "The field is not null!"
      End If
   End Function

   Function IsFieldNull (MyValue As Variant)
      If IsNull(MyValue) Then
         IsFieldNull = "The field is null!"
      Else
         IsFieldNull = "The field is not null!"
      End If
   End Function