[] is not a 40-byte hex string

[stepancheg]

Occasionally, once every few days, command fail like this, and on retry the command is successful like nothing happens.

$ sl pull --rebase
pulling from ssh://[email protected]/xxx/yyy.git
remote: Enumerating objects: 15, done.
remote: Counting objects: 100% (15/15), done.
remote: Compressing objects: 100% (2/2), done.
remote: Total 8 (delta 7), reused 6 (delta 6), pack-reused 0 (from 0)
Receiving objects: 100% (8/8), 1.31 KiB | 268.00 KiB/s, done.
Resolving deltas: 100% (7/7), completed with 7 local objects.
From ssh://github.com/xxx/yyy
   24cf70cad..db8e63378  db8e63378fd006c911846ef9a0ed76a462bc13d8 -> origin/main
warning: failed to inspect working copy parent
abort: When constructing alloc::boxed::Box<dyn commits_trait::DagCommits + core::marker::Send> from dyn storemodel::StoreInfo, "10-git-commits" reported error

Caused by:
    [] is not a 40-byte hex string

The bug may be hard to fix, but condier adding diagnostics there so next time it would be more clear where it comes from.