new toolkit tree functions

action.go

@@ -101,7 +101,11 @@ func (me *TreeInfo) doAction(a widget.Action) {
 	case widget.Disable:
 		me.Disable(n)
 	case widget.Delete:
-		me.Hide(n)
+		if me.Hide == nil {
+			log.Info("toolkit doesn't know how to Hide() widgets")
+		} else {
+			me.Hide(n)
+		}
 		log.Info("tree: todo: remove child from parent")
 		n.DeleteNode()
 		// now remove the child from the parent