detect None values in workflow

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@35796 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5Type/XMLExportImport.py

@@ -139,8 +139,11 @@ def Base_asXML(object, root=None):
             variable_type = "date"
           if workflow_variable.find('language_revs') >= 0: # XXX specific to cps
             variable_type = "dict"
+          if workflow_action[workflow_variable] is None:
+            variable_type = 'None'
           variable_node = SubElement(workflow_node, workflow_variable,
                                      attrib=dict(type=variable_type))
+          if variable_type != 'None':
             variable_node_text = str(workflow_action[workflow_variable])
             variable_node.text = unicode(variable_node_text, 'utf-8')