cloud - How to override action Email SalesOrder in SO30100 Screen -

i try customize action email in salesorder screen, use code not work. give me suggest code , customize send notification in acumatica. using acumatica 4.2. thank in advance.

    public cractivitylist<soorder>    activity;      public pxaction<soorder> notification;      [pxuifield(displayname = "notifications", visible = false)]     [pxbutton(imagekey = px.web.ui.sprite.main.dataentryf)]     protected virtual ienumerable notification(pxadapter adapter,         [pxstring] string notificationcd         )     {         foreach (soorder order in adapter.get<soorder>())         {             if (order.ordertype == "cm")             {                 ///my function                 emailnotification.send_atnpp(order, "so301000", "sendreturnso", "[[noidung]]", createemailcontent(order));             }             yield return order;         }         yield return adapter.get();     } 

what error receive? have tried removing final yield? last line can

return adapter.get();