--- a/server/mssteps.py	Thu Jun 17 18:50:20 2010 +0200
+++ b/server/mssteps.py	Fri Jun 18 08:14:00 2010 +0200
@@ -21,8 +21,8 @@
 * get data from the parent plan, the latest step, temporary table...
 * each step has is own members (this is not necessarily bad, but a bit messy
   for now)
+"""
 
-"""
 __docformat__ = "restructuredtext en"
 
 from rql.nodes import VariableRef, Variable, Function
@@ -37,11 +37,11 @@
     for select in union.children:
         if keepgroup:
             having, orderby = select.having, select.orderby
-            select.having, select.orderby = None, None
+            select.having, select.orderby = (), ()
             clauses.append( (having, orderby) )
         else:
             groupby, having, orderby = select.groupby, select.having, select.orderby
-            select.groupby, select.having, select.orderby = None, None, None
+            select.groupby, select.having, select.orderby = (), (), ()
             clauses.append( (groupby, having, orderby) )
     return clauses