diff -r b55747ca518f -r f6874567a93b mercurial/commands.py
--- a/mercurial/commands.py	Thu Sep 27 22:07:12 2018 -0400
+++ b/mercurial/commands.py	Wed Sep 26 22:17:26 2018 -0700
@@ -1224,7 +1224,7 @@
                                 "a destination"))
         if opts.get('base'):
             ui.warn(_("ignoring --base because --all was specified\n"))
-        base = ['null']
+        base = [nullrev]
     else:
         base = scmutil.revrange(repo, opts.get('base'))
     if cgversion not in changegroup.supportedoutgoingversions(repo):