importer fails to find “main” branch on github

Backtrace:

In guix/ui.scm:

1374:6 19 (guix-import-cran . _)

In ice-9/boot-9.scm:

1752:10 18 (with-exception-handler _ _ #:unwind? _ #:unwind-for-type _)

In guix/scripts/import/cran.scm:

121:31 17 (_)

In guix/import/utils.scm:

647:27 16 (recursive-import _ #:repo->guix-package _ #:guix-name _ #:version _ . _)

639:33 15 (lookup-node "https://github.com/zdebruine/singlet" #f)

In guix/memoization.scm:

98:0 14 (mproc "https://github.com/zdebruine/singlet" #:version #f #:repo git #:repo->guix-package #<procedure mproc args> #:guix-name …)

In unknown file:

13 (_ #<procedure 7f75548c7760 at guix/memoization.scm:179:32 ()> #<procedure list _> (this is nothing))

In guix/import/cran.scm:

748:24 12 (_ "https://github.com/zdebruine/singlet" #:repo _ #:version _ #:license-prefix _ #:fetch-description _ #:download-source _)

320:25 11 (fetch-description _ "https://github.com/zdebruine/singlet" _)

In guix/memoization.scm:

98:0 10 (mproc "https://github.com/zdebruine/singlet" #:method git)

In unknown file:

9 (_ #<procedure 7f75548c76c0 at guix/memoization.scm:179:32 ()> #<procedure list _> (this is nothing))

In ice-9/boot-9.scm:

1752:10 8 (with-exception-handler _ _ #:unwind? _ #:unwind-for-type _)

In guix/store.scm:

659:37 7 (thunk)

In guix/git.scm:

562:8 6 (latest-repository-commit #<store-connection 256.99 7f75534a4820> "https://github.com/zdebruine/singlet" #:recursive? _ # _ # _ …)

291:4 5 (update-cached-checkout _ #:ref _ #:recursive? _ #:check-out? _ #:starting-commit _ #:log-port _ #:cache-directory _)

241:18 4 (resolve _)

In git/reference.scm:

60:8 3 (_ _ _)

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: reference 'refs/remotes/origin/HEAD' not found