for e in log:
    if e.commitid:

• mindate[e.commitid] = min(e.date, mindate.get(e.commitid))

+ if mindate.get(e.commitid) is None:
+ mindate[e.commitid] = None
+ else:
+ mindate[e.commitid] = min(e.date, mindate.get(e.commitid))

1. Merge changesets log.sort(key=lambda x: (mindate.get(x.commitid), x.commitid, x.comment,

mindate is also used here as a comparison key. Filling it to None would
make things worse.

I think the original code, which just fills every mindate element with None,
was wrong. Instead, it should probably keep the minimum value only if exists,

if e.commitid in mindate:
    mindate[e.commitid] = min(e.date, mindate[e.commitid])
else:
    mindate[e.commitid] = e.date

and later falls back to the null value.

log.sort(key=lambda x: (mindate.get(x.commitid, (lowest_or_highest_value?, 0)