Free5gc-compose repo, 'make base' fails: 'apt-get update' opening configuration file /etc/apt/apt.conf.d/01autoremove - ifstream::ifstream (13: Permission denied)

Hi,
I’m following https://github.com/free5gc/free5gc-compose
I’m on ubuntu 18.04
and my kernel is 5.0.0-23-generic

in below section:

Run Up

with even root user (su -i), 'make base’ fails with below error:

$ make base
in the actual command being ran (docker build xxxx):
apt-get update opening configuration file /etc/apt/apt.conf.d/01autoremove - ifstream::ifstream (13: Permission denied)

would you pls help.