[INFO] cloning repository https://github.com/wangjun861205/juju-backend
[INFO] running `Command { std: "git" "-c" "credential.helper=" "-c" "credential.helper=/workspace/cargo-home/bin/git-credential-null" "clone" "--bare" "https://github.com/wangjun861205/juju-backend" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fwangjun861205%2Fjuju-backend", kill_on_drop: false }`
[INFO] [stderr] Cloning into bare repository '/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fwangjun861205%2Fjuju-backend'...
[INFO] running `Command { std: "git" "rev-parse" "HEAD", kill_on_drop: false }`
[INFO] [stdout] 7d356b0c5505d688056b2f9badabb6ce76c2e0a5
[INFO] checking wangjun861205/juju-backend against master#8a65ee08296b36342bf7c3cdc15312ccbc357227 for pr-142704
[INFO] running `Command { std: "git" "clone" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fwangjun861205%2Fjuju-backend" "/workspace/builds/worker-0-tc1/source", kill_on_drop: false }`
[INFO] [stderr] Cloning into '/workspace/builds/worker-0-tc1/source'...
[INFO] [stderr] done.
[INFO] [stderr] fatal: update_ref failed for ref 'HEAD': cannot update ref 'refs/heads/master': couldn't write '/workspace/builds/worker-0-tc1/source/.git/refs/heads/master.lock'


failed to checkout https://github.com/wangjun861205/juju-backend

Caused by:
    command failed: exit status: 128