--- a/hgext3rd/evolve/firstmergecache.py	Wed Jul 17 11:45:37 2019 -0700
+++ b/hgext3rd/evolve/firstmergecache.py	Thu Jul 11 15:30:43 2019 -0700
@@ -74,16 +74,17 @@
         cl = repo.unfiltered().changelog
         total = len(data)
 
-        def progress(pos, rev):
+        def progress(pos, rev=None):
+            revstr = '' if rev is None else ('rev %d' % rev)
             compat.progress(repo.ui, 'updating firstmerge cache',
-                            pos, 'rev %s' % rev, unit='revision', total=total)
-        progress(0, '')
+                            pos, revstr, unit='revision', total=total)
+        progress(0)
         for idx, rev in enumerate(data, 1):
             assert rev == len(self._data), (rev, len(self._data))
             self._data.append(self._firstmerge(cl, rev))
             if not (idx % 10000): # progress as a too high performance impact
                 progress(idx, rev)
-        progress(None, '')
+        progress(None)
 
     def _firstmerge(self, changelog, rev):
         cl = changelog