How stop routine if text field is left blank

I have a form which contains a command button.  Also on this form is a text field.  When the command button is clicked and if the text field is left blank I want the routine to stop and make the user enter a value in the text field.  Here is my attempt...

    If Me.txtPOn = "" Then
        MsgBox "You must enter a PO number first!"
        Me.txtPOn.SetFocus
    End If

But what is happening is the record is getting written to the table because of code after the above code.  This is not what I want to have happen.  Instead, the whole routine should halt and the focus should be on the text box.. "txtPOn".

I can't figure out how to make this happen.  Can someone help?

--Steve
SteveL13Asked:
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Dale FyeOwner, Developing Solutions LLCCommented:
Steve,

It is likely that if no data has ever been entered into the txtPOn control, that the "value" of that control is NULL, and whenever you try to compare a NULL to anything, it will fail, so you should either use:

IF me.txtPOn & "" = "" Then

or you could use

If NZ(me.txtPOn, "") = "" Then
NatchiketCommented:
You need to exit the procedure rather than carrying on with the code, thus

If Nz(Me.txtPOn,vbNullstring) = vbNullstring Then
        MsgBox "You must enter a PO number first!"
        Me.txtPOn.SetFocus
        Exit Sub
End If

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SteveL13Author Commented:
This worked perfectly.  Thank you for your help.
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