I want to control null layers that have their position directly parented (via expression) by using a

I parented the position of the puppet pin 'L1' to the null layer 'L1',
and the pin 'L2' to the null layer 'L2'.
The expression used is: thisComp.layer("L1").transform.position

Then, I parented both null layers 'L1' and 'L2' to the null layer 'L' to control them together
(using the pick whip in the "Parent & Link" section to link the layers themselves, not just the position).

However, the control doesn’t work.
The null layer 'L' does not affect them as expected.