--- a/mercurial/merge.py	Tue Dec 12 17:52:33 2006 -0600
+++ b/mercurial/merge.py	Tue Dec 12 18:16:23 2006 -0600
@@ -441,6 +441,9 @@
     wlock = working dir lock, if already held
     """
 
+    if node is None:
+        node = "tip"
+
     if not wlock:
         wlock = repo.wlock()