diff --git a/extra/modules/configuration.py b/extra/modules/configuration.py
index 1a13dd8..1e0166c 100644
--- a/extra/modules/configuration.py
+++ b/extra/modules/configuration.py
@@ -5,19 +5,23 @@ presentation_args = { 'cols': 80, 'rows': 25 }
 for schema in (String('xmlrpc_registration_url',
             N_('XMLRPC Neogia registration URL'),
             default = '',
+            allow_none=True,
             presentation_hint = { 'args': { 'size': 100 }}),
         String('erp_secret',
             N_('Shared secret with the ERP'),
             default = '',
+            allow_none=True,
             presentation_hint = { 'args': { 'size': 100 }}),
         String('cnil_text',
             N_("Texte d'information CNIL"),
             default = '',
+            allow_none=True,
             presentation_hint = { 'widget': 'Text',
                 'args': presentation_args }),
         String('condition_utilisation',
             N_("Condition d'utilisation"),
             default = '',
+            allow_none=True,
             presentation_hint = { 'widget': 'Text',
                 'args': presentation_args })):
     configuration.identity_configuration.add_schema(schema)