Action PressButton via Business Event causes NullReferenceException

The below event works fine when the UI button is pressed, however when a business event calls it the PressButton() function returns a NullRefernceException. I can not figure out why.

the exception stack is

   at PX.Data.PXAction`1.<Press>d__38.MoveNext()
   at PX.Data.GraphHelper.PressButton(PXAction action, PXAdapter adapter)
   at GPGeneral.PM.PMTaskEntry_Ext.SendPendingNotifications(PXAdapter adapter) in C:\Program Files\Acumatica ERP\ACU-1\App_Data\Projects\GPGeneral\GPGeneral\PM\Task\PMTaskEntry_Ext.cs:line 511
   at PX.Data.PXAction`1.RunHandler(PXAdapter adapter)
   at PX.Data.PXAction`1.<Press>d__38.MoveNext()

        public PXAction<PMTask> sendPendingNotifications;

        [PXUIField(DisplayName = "Send Pending Notifications", MapEnableRights = PXCacheRights.Update, MapViewRights = PXCacheRights.Select, Enabled = true)]
        [PXButton(CommitChanges = true, Category = "Notify", Connotation = PX.Data.WorkflowAPI.ActionConnotation.None)]//, ImageKey = Sprite.Main.Preview)]
        public IEnumerable SendPendingNotifications(PXAdapter adapter)
        {
            var task = Base.Task.Current;
            if (task != null)
            {
                var task_Ext = task.GetExtension<PMTask_Ext>();
                var existingNotifications = Notifications.Select().RowCast<GPTaskNotificationRecord>().ToList();

                foreach (var item in existingNotifications)
                {
                    if (item.DelayedSend == true)
                    {
                        var emailGraph = createTaskEmailGraph(task, item, item.DelayedSendCrew ?? task_Ext.UsrPrimaryCrewID);
                        emailGraph.Send.PressButton();
                        updateNotificationSentStats(item);
                    }
                }

            }
            return adapter.Get();
        }

private CREmailActivityMaint createTaskEmailGraph(PMTask tsk, GPTaskNotificationRecord notRec, int? crewID)
        {
            var not = GPTaskNotification.PK.Find(Base, notRec.TaskNotificationID);
            var noteTemplate = Notification.PK.Find(Base, not.EmailTemplateID);
            if (noteTemplate == null)
                throw new PXException($"Notification template '{not.EmailTemplateID}' is missing");


            CREmailActivityMaint emailMaint = PXGraph.CreateInstance<CREmailActivityMaint>();
            var email = emailMaint.Message.Insert(new CRSMEmail()
            {
                MailTo = emailToMerge(noteTemplate.NTo, crewID),
                MailCc = emailToMerge(noteTemplate.NCc, crewID),
                MailBcc = emailToMerge(noteTemplate.NBcc, crewID),
                Subject = emailMerge(noteTemplate.Subject, crewID),
                Body = emailMerge(noteTemplate.Body, crewID),
                RefNoteIDType = typeof(PMTask).ToString(),
                RefNoteID = tsk.NoteID
                //RefNoteID = task.NoteID,
            });

            if (noteTemplate.NFrom != null)
                email.MailAccountID = noteTemplate.NFrom;

            PXNoteAttribute.CopyNoteAndFiles(Base.Caches<Notification>(), noteTemplate, emailMaint.Message.Cache, email, false, true);


            }
            return emailMaint;
        }