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

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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 you use the following function 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
				

To prevent the error "Invalid Use of Null!" or "#Error" when the field is null, define the variable, MyValue, in the custom IsFieldNull() function as a Variant, as follows:

   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