--- a/hgext/evolve.py	Thu Mar 17 11:31:55 2016 -0700
+++ b/hgext/evolve.py	Thu Mar 17 15:04:05 2016 -0700
@@ -2002,7 +2002,7 @@
         hg.update(repo, divergent.rev())
     repo.ui.note(_('merging divergent changeset\n'))
     if progresscb: progresscb()
-    if 'partial' in merge.update.__doc__:
+    if merge.update.__doc__ is not None and 'partial' in merge.update.__doc__:
         # Mercurial  < 43c00ca887d1 (3.7)
         stats = merge.update(repo,
                              other.node(),