$ sudo guix system reconfigure /etc/config.scm
Password: 
Backtrace:
In guix/ui.scm:
  2286:10 19 (run-guix-command _ . _)
In ice-9/boot-9.scm:
  1752:10 18 (with-exception-handler _ _ #:unwind? _ # _)
In guix/status.scm:
    859:3 17 (_)
    839:4 16 (call-with-status-report _ _)
In guix/scripts/system.scm:
   1278:4 15 (_)
In ice-9/boot-9.scm:
  1752:10 14 (with-exception-handler _ _ #:unwind? _ # _)
In guix/store.scm:
   659:37 13 (thunk)
   1298:8 12 (call-with-build-handler #<procedure 7f20532e8b40 at g…> …)
  2168:25 11 (run-with-store #<store-connection 256.99 7f2057bfd410> …)
In guix/scripts/system.scm:
  1302:15 10 (_ _)
    831:5  9 (perform-action reconfigure #<<image> name: #f format:…> …)
In guix/scripts/system/reconfigure.scm:
    346:3  8 (check-forward-update _ #:current-channels _)
In srfi/srfi-1.scm:
   691:23  7 (filter-map #<procedure 7f205894eba0 at guix/scripts…> . #)
In guix/scripts/system/reconfigure.scm:
   353:39  6 (_ #<<channel> name: guix url: "https://git.savannah.gn…>)
In guix/git.scm:
   481:21  5 (update-cached-checkout _ #:ref _ #:recursive? _ # _ # _ …)
   367:15  4 (reference-available? _ _)
In git/commit.scm:
    172:8  3 (_ #<git-repository 24fd030> #<oid 4f35ff1275e05be31f5d…>)
In git/bindings.scm:
     77:2  2 (raise-git-error _)
In ice-9/boot-9.scm:
  1685:16  1 (raise-exception _ #:continuable? _)
  1685:16  0 (raise-exception _ #:continuable? _)

ice-9/boot-9.scm:1685:16: In procedure raise-exception:
Git error: object not found - no match for id (4f35ff1275e05be31f5d41464ccf147e9dbfd016)