mercurial/revset.py

--- a/mercurial/revset.py	Fri Oct 10 17:28:18 2014 -0700
+++ b/mercurial/revset.py	Sat Oct 11 01:39:20 2014 -0700
@@ -1132,7 +1132,10 @@
         if pm is not None:
             rn = repo.changelog.rev(pm)
 
-    return subset.filter(lambda r: r == rn)
+    if rn is None:
+        return baseset()
+    result = baseset([rn])
+    return result & subset
 
 def obsolete(repo, subset, x):
     """``obsolete()``