Error after reparent node

Question

I'm trying to use reparent but I get an error after reparenting.

func on_redBalls_pressed(viewport, event, shape_idx):
    if event is InputEventMouseButton:
        if event.button_index == BUTTON_LEFT and not event.is_echo() and event.is_pressed():
            print("pressed")
            temp_parenting($RedBalls, $RedZone)


func temp_parenting(child, new_parent):
    for i in $RedZone/RedPositions.get_children().size():
        if child.global_position == $RedZone/RedPositions.get_child(i).global_position:
            var old_parent = child.get_parent()
            old_parent.remove_child(child)
            child.position = $RedZone/RedPositions.get_child(i).position
            new_parent.add_child(child)
            new_parent.set_owner(child)
            break

When the method called first time works, but then I get error when the function called the second time because "child" is null.

Answer 1

I' ll answer myself because I found what was wrong with above. I'm running on mouse press, so after the reparenting is done, the $RedBall node has a new parent so it doesn't exist any more in the old parent. So the second time gives the null error.
I changed the code and I first checking if the node exists, then run the function and no works fine.