Systemd gitlab-runner.service file fails with gitlab-runner: FATAL: the "HOME" is not set

systemctl start fails to start the gitlab-runner both on boot and on execution of systemctl start gitlab-runner.service

Running the service file on the command line works. Here’s the gitlab-runner.service file;

[Unit]
Description=GitLab Runner
After=syslog.target network.target
ConditionFileIsExecutable=/usr/local/bin/gitlab-runner

[Service]
StartLimitInterval=5
StartLimitBurst=10
ExecStart=/usr/local/bin/gitlab-runner "run" "--working-directory" "/home/gitlab-runner" "--service" "gitlab-runner" "--syslog" "--user" "gitlab-runner"

Restart=always
RestartSec=120

[Install]
WantedBy=multi-user.target

journalctl shows;

 VERSION:   12.10.2 (c5874a4b)
gitlab-runner[44116]: FATAL: the "HOME" is not set                      
Jun 12 04:33:26 skull.jeremiahfoster.com systemd[1]: gitlab-runner.service: Main process exited, code=exited, status=1/FAILURE
Jun 12 04:33:26 skull.jeremiahfoster.com systemd[1]: gitlab-runner.service: Failed with result 'exit-code'.

How does one set the “HOME”? Where is this error coming from? gitlab-runner executable? The shell?