Check For Null In Repeater Date Field

I'm about ready to pull my hair out.  
I have a repeater control, and a date field.  If the field is a valid date, I'll use it to calculate and display the person's age.  Otherwise, I want to display "N/A".  My problem is trying to determine if the date field is null or not.
I'm using SQL Server 2005 which allows Nulls in the date field, and for many records I don't have a birth date.  It makes sense for these records to leave the date Null.  
This is my code:
Protected Sub Repeater1_ItemDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.RepeaterItemEventArgs) Handles Repeater1.ItemDataBound
    If e.Item.ItemType = ListItemType.Item OrElse e.Item.ItemType = ListItemType.AlternatingItem Then
        Dim LabelIcon As Label = CType(e.Item.FindControl("LabelIcon"), Label)
        Dim LblAge As Label = CType(e.Item.FindControl("LblAge"), Label)
        Dim inmate As WAP.prisonmembersRow = CType(CType(e.Item.DataItem, System.Data.DataRowView).Row, WAP.prisonmembersRow)
        If System.IO.File.Exists(Server.MapPath("~/images/picts/" & inmate.FILE2 & ".jpg")) Then
            LabelIcon.Visible = True
        End If
        If inmate.DATE_OF_BIRTH Is DBNull.Value Then
            If IsDate(inmate.DATE_OF_BIRTH) Then
                LblAge.Text = "Age: N/A"
            Else
                LblAge.Text = "Age: " & GetBirthdate(inmate.DATE_OF_BIRTH)
            End If
        End If
    End If
End Sub
How can I resolve this?
Diane