--- a/hgext3rd/topic/revset.py	Thu Jun 22 09:46:30 2017 +0200
+++ b/hgext3rd/topic/revset.py	Thu Jun 22 09:41:01 2017 +0200
@@ -39,9 +39,16 @@
     else:
         matcher = lambda t: bool(t)
     mutable = repo._phasecache.getrevset(repo, (phases.draft, phases.secret))
-    drafts = subset & mutable
-    return drafts.filter(
-        lambda r: matcher(repo[r].extra().get(constants.extrakey, '')))
+
+    rawchange = repo.changelog.changelogrevision
+    key = constants.extrakey
+
+    def matchtopic(r):
+        topic = rawchange(r).extra.get(key)
+        if topic is None:
+            return False
+        return matcher(topic)
+    return (subset & mutable).filter(matchtopic)
 
 def ngtipset(repo, subset, x):
     """`ngtip([branch])`