Use nullrev+count instead of count-1 in a newly introduced expression. Before that repo.changelog.tip() was used, but this yields a node. Of course many more places should be changed like this, this was just done as an example.

0 files updated, 0 files merged, 0 files removed, 0 files unresolved
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
adding b
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
adding b