building through docker

[akbwyfc]

Hi All,

I'm new to Tristan-MP and docker as well.
I'm trying to build the code through docker, but I receive the error:
=> ERROR [ 6/12] RUN useradd -ms /bin/zsh root 0.2s

[ 6/12] RUN useradd -ms /bin/zsh root:
0.159 useradd: user 'root' already exists

---

Dockerfile:19

17 | rm -rf /var/lib/log/*
18 |
19 | >>> RUN useradd -ms /bin/zsh $USERNAME
20 | RUN usermod -aG sudo $USERNAME
21 | RUN echo '%sudo ALL=(ALL) NOPASSWD:ALL' >> /etc/sudoers

ERROR: failed to solve: process "/bin/sh -c useradd -ms /bin/zsh $USERNAME" did not complete successfully: exit code: 9
ERROR: Service 'tristanv2' failed to build : Build failed

Thanks in advance for your help.
Cheers