mercurial/merge.py

--- a/mercurial/merge.py	Mon Nov 21 21:51:23 2016 -0500
+++ b/mercurial/merge.py	Mon Nov 21 21:52:19 2016 -0500
@@ -25,7 +25,6 @@
 )
 from . import (
     copies,
-    destutil,
     error,
     filemerge,
     obsolete,
@@ -1484,11 +1483,6 @@
         if ancestor is not None:
             pas = [repo[ancestor]]
 
-        if node is None:
-            repo.ui.deprecwarn('update with no target', '3.9')
-            rev, _mark, _act = destutil.destupdate(repo)
-            node = repo[rev].node()
-
         overwrite = force and not branchmerge
 
         p2 = repo[node]