Nulls and While dr.Read question

[BukHix]

I am pulling some data to my form from a SQL Server database. I have one field that sometimes has a value and other times has a null. If I try to use the following code I get an error if the class field is null in the database. How can I adjust this code to accept null values if need be?

dr = cmd.ExecuteReader
        If dr.HasRows Then
            While dr.Read()
                txtFName.Text = dr("FirstName")
                txtLName.Text = dr("LastName")
                txtRate.Text = Format(dr("HrlyRate"), "Fixed")
                txtBaseRate.Text = Format(dr("HrlyRate"), "Fixed")
                txtPrDept.Text = dr("PRDept")
                txtCrew.Text = dr("Crew")
                txtClass.Text = dr("Class")