Not getting expected results from state.get_contact_impulse() function

I'm trying to access the impulse vector, when two RigidBody2D objects colloid.
For this I wrote this in my RigidBody2D gdscript:

The problem is, when there's a collision and I see the print "APPLIED IMPULSE", I always get 0 for state.get_contact_impulse(0)
why is that? I'm expecting it to be printed for each colliding object and display the impulse applied to them because of the collision.

There are only two objects of type RigidBody2D, names pen_fighter, and pen_fighter2. I'm attaching the log I see for this code when these two objects colloid: