diff -r 56eed3923dbc -r 947771ad5174 mercurial/copies.py
--- a/mercurial/copies.py	Tue May 26 23:14:50 2015 +0900
+++ b/mercurial/copies.py	Fri May 22 14:02:04 2015 -0700
@@ -370,6 +370,7 @@
 
     # generate a directory move map
     d1, d2 = c1.dirs(), c2.dirs()
+    # Hack for adding '', which is not otherwise added, to d1 and d2
     d1.addpath('/')
     d2.addpath('/')
     invalid = set()