mercurial/scmutil.py

--- a/mercurial/scmutil.py	Sun Apr 08 09:28:49 2018 -0700
+++ b/mercurial/scmutil.py	Sun Apr 08 09:28:08 2018 -0700
@@ -503,7 +503,7 @@
             rev = repo.changelog.rev(node)
             return repo[rev]
 
-        return repo[symbol]
+        raise error.RepoLookupError(_("unknown revision '%s'") % symbol)
 
     except error.WdirUnsupported:
         return repo[None]