diff -r 5cac3accdaa1 -r 2d15c59a001b mercurial/wireproto.py
--- a/mercurial/wireproto.py	Mon Apr 06 17:23:11 2015 -0700
+++ b/mercurial/wireproto.py	Tue Apr 07 16:01:32 2015 -0700
@@ -363,7 +363,9 @@
             opts[key] = value
         f = self._callcompressable("getbundle", **opts)
         bundlecaps = kwargs.get('bundlecaps')
-        if bundlecaps is not None and 'HG2Y' in bundlecaps:
+        if bundlecaps is None:
+            bundlecaps = () # kwargs could have it to None
+        if util.any((cap.startswith('HG2') for cap in bundlecaps)):
             return bundle2.getunbundler(self.ui, f)
         else:
             return changegroupmod.cg1unpacker(f, 'UN')