antis81/libqgit2 — comment on commit a490f8b58a4f0515b39b61faacd8880edcaac448
File:  line 0
By ropez:

Also:

QGitOId oid = QGitOId::fromString("badbadbadbadbadbadbadbadbadbadbadbadbadbad");
oid.isValid(); // true
repo.lookupCommit(oid); // fails