Send a null value to a database (conditional)

[BukHix]

How I do I send an actual null value to an SQL database? Right now I am sending a empty string but I have to change that to a null. I thought something like this would work but I must be missing something.

Dim strCityTax As String
 
        If txtCityTax.Text = "" Then
            strCityTax = DBNull
        Else
            strCityTax = txtCityTax.Text
        End If

That puts a squiggly line under the DBNull with this warning: 'DBNull' is a type and cannot be used as an expression.