--- a/mercurial/revset.py	Wed Oct 15 12:38:47 2014 -0700
+++ b/mercurial/revset.py	Wed Oct 08 02:45:21 2014 -0700
@@ -398,7 +398,7 @@
     args = getargs(x, 1, 2, _('only takes one or two arguments'))
     include = getset(repo, spanset(repo), args[0])
     if len(args) == 1:
-        if len(include) == 0:
+        if not include:
             return baseset()
 
         descendants = set(_revdescendants(repo, include, False))