diff --git a/test/test_parsing_group.py b/test/test_parsing_group.py
index 992a3f8..d28c59e 100644
--- a/test/test_parsing_group.py
+++ b/test/test_parsing_group.py
@@ -9,7 +9,7 @@ def make_description():
     nombre_interfaces = IntOption('nombre_interfaces', "nombre d'interfaces à activer",
                                    default=1)
     activer_proxy_client = BoolOption('activer_proxy_client', "utiliser un proxy",
-                                      default=False) 
+                                      default=False)
     mode_conteneur_actif = BoolOption('mode_conteneur_actif', "le serveur est en mode conteneur",
                                       default=False)
 #    hidden (variable cachée)
@@ -25,9 +25,9 @@ def make_description():
     interface1 = OptionDescription('interface1', '', [master])
     interface1.set_group_type('group')
 
-    general = OptionDescription('general', '', [numero_etab, nom_machine, 
+    general = OptionDescription('general', '', [numero_etab, nom_machine,
                                              nombre_interfaces, activer_proxy_client,
-                                             mode_conteneur_actif, adresse_serveur_ntp, 
+                                             mode_conteneur_actif, adresse_serveur_ntp,
                                              time_zone])
     general.set_group_type('family')
     creole = OptionDescription('creole', 'first tiramisu configuration', [general, interface1])
@@ -39,7 +39,7 @@ def test_base_config():
     config = Config(descr)
     assert config.creole.general.activer_proxy_client == False
     assert config.creole.general.nom_machine == "eoleng"
-    assert config.get('nom_machine') == "eoleng"    
+    assert config.get('nom_machine') == "eoleng"
     result = {'general.numero_etab': None, 'general.nombre_interfaces': 1,
     'general.serveur_ntp': [], 'interface1.ip_admin_eth0.ip_admin_eth0': None,
     'general.mode_conteneur_actif': False, 'general.time_zone': 'Paris',
@@ -67,4 +67,13 @@ def test_iter_on_groups():
     result = list(config.creole.iter_groups())
     group_names = [res[0] for res in result]
     assert group_names == ['general', 'interface1']
-    
+
+def test_iter_on_empty_group():
+    config = Config(OptionDescription("name", "descr", [] ))
+    result = list(config.iter_groups())
+    assert result == []
+    for i in config.iter_groups():
+        pass
+    for i in config:
+        pass
+    assert [] == list(config)
diff --git a/tiramisu/config.py b/tiramisu/config.py
index b7b3252..ed5c881 100644
--- a/tiramisu/config.py
+++ b/tiramisu/config.py
@@ -209,6 +209,16 @@ class Config(object):
             return True
         return False
 
+    def _test_mandatory(self, path, opt):
+        # mandatory options
+        homeconfig = self._cfgimpl_get_toplevel()
+        mandatory = homeconfig._cfgimpl_mandatory
+        if opt.is_mandatory() and mandatory:
+            if self._is_empty(opt) and \
+                    opt.is_empty_by_default():
+                raise MandatoryError("option: {0} is mandatory "
+                                      "and shall have a value".format(path))
+
     def __getattr__(self, name):
         return self._getattr(name)
 
@@ -299,15 +309,7 @@ class Config(object):
                         raise ConfigError('invalid calculated value returned'
                             ' for option {0}'.format(name))
                     self._cfgimpl_values[name] = _result
-
-            # mandatory options
-            homeconfig = self._cfgimpl_get_toplevel()
-            mandatory = homeconfig._cfgimpl_mandatory
-            if opt_or_descr.is_mandatory() and mandatory:
-                if self._is_empty(opt_or_descr) and \
-                        opt_or_descr.is_empty_by_default():
-                    raise MandatoryError("option: {0} is mandatory "
-                                          "and shall have a value".format(name))
+            self._test_mandatory(name, opt_or_descr)
             # frozen and force default
             if not opt_or_descr.has_callback() and opt_or_descr.is_forced_on_freeze():
                 return opt_or_descr.getdefault()
@@ -577,11 +579,11 @@ class Config(object):
             groups = [group_type]
         for child in self._cfgimpl_descr._children:
             if isinstance(child, OptionDescription):
-                    try:
-                        if child.get_group_type() in groups:
-                            yield child._name, getattr(self, child._name)
-                    except:
-                        pass # hidden, disabled option
+                try:
+                    if child.get_group_type() in groups:
+                        yield child._name, getattr(self, child._name)
+                except:
+                    pass # hidden, disabled option
     # ______________________________________________________________________
     def __str__(self, indent=""):
         "Config's string representation"
@@ -742,7 +744,15 @@ def mandatory_warnings(config):
     config._cfgimpl_get_toplevel()._cfgimpl_mandatory = True
     for path in config._cfgimpl_descr.getpaths(include_groups=True):
         try:
-            value = getattr(config, path)
+            if '.' in path:
+                homeconfig, path = config._cfgimpl_get_home_by_path(path)
+            else:
+                homeconfig = config
+            opt = getattr(homeconfig._cfgimpl_descr, path)
+            #for PropertiesOptionError
+            homeconfig._validate(path, opt)
+            if not isinstance(opt, OptionDescription):
+                homeconfig._test_mandatory(path, opt)
         except MandatoryError:
             yield path
         except PropertiesOptionError: