--- a/web/views/basecontrollers.py	Wed Dec 09 15:51:20 2015 +0100
+++ b/web/views/basecontrollers.py	Tue Dec 08 16:27:05 2015 +0100
@@ -128,7 +128,7 @@
         view, rset = self._select_view_and_rset(rset)
         view.set_http_cache_headers()
         if self._cw.is_client_cache_valid():
-            return ''
+            return b''
         template = self.appli.main_template_id(self._cw)
         return self._cw.vreg['views'].main_template(self._cw, template,
                                                     rset=rset, view=view)