Exit sub without triggering AfterUpdate

Hello,

I have disabled the X on my userform and have an added a exit button on the form. I routine in the txtStudentID_AfterUpdate() field. If the user enters their studentID in that field and then deletes/backspace and tries to exit the form, the routine still runs. I just want it to allow the user to exit. They basically have to hit exit twice. I played around with this for a while and just can't figure out how to get around it. Don't want the user to msgbox when exiting.

 Private Sub txtEmpNumber_AfterUpdate()
'Connects to dba 
Dim rs As Object, strSQL As String

    ' connect to the Access database
    Set cn = New ADODB.Connection
    myConn = TARGET_DB
    With cn
     .Provider = "Microsoft.ACE.OLEDB.12.0"
     .Open myConn
   End With

'create recordset
Set rs = New ADODB.Recordset

src = "SELECT StudentName FROM qryStudentDB WHERE [StudentID]='" & Me.txtStudentID.Value & "'"

Set rs = New ADODB.Recordset

rs.Open src, cn, adOpenStatic

If rs.RecordCount = 0 Then
    rs.Close
    Set myConn = Nothing
    Set rs = Nothing
    MsgBox "No Records Found"
'    Me.txtStudentID.SetFocus
    Exit Sub
End If

txtStudentName.Text = rs(0)

Set rs = Nothing

End Sub

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Exit Button

Private Sub cmdExit_Click()
Unload Me
 End Sub

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