Joint_states msg not being used for state estimation?

[mudrole1]

I am running a legged robot in Gazebo sim, hence /joint_states are published by the Gazebo, rather than by the quadruped_controller. I wanted to use the topic /base_to_footprint_pose to get the dynamic transformation between /base_link and /base_footprint. The issue is that it doesn't change and it is the max length of the leg. Upon further investigation, I can see that the state_estimation_node subscribe to /joint_states but there is no associated callback to it, i.e. the msg are ignored. Or am i completely wrong? See line 38 on https://github.com/chvmp/champ/blob/master/champ_base/src/state_estimation.cpp

What is the intended logic here?