diff --git a/tiramisu/option/portoption.py b/tiramisu/option/portoption.py
index c277344..eb36517 100644
--- a/tiramisu/option/portoption.py
+++ b/tiramisu/option/portoption.py
@@ -19,11 +19,8 @@
 # the whole pypy projet is under MIT licence
 # ____________________________________________________________
 import re
-import sys
 
-from ..setting import undefined, Undefined, OptionBag
 from ..i18n import _
-from .option import Option
 from .stroption import StrOption
 
 
diff --git a/tiramisu/setting.py b/tiramisu/setting.py
index 36a4abe..50e25df 100644
--- a/tiramisu/setting.py
+++ b/tiramisu/setting.py
@@ -117,6 +117,7 @@ FORBIDDEN_SET_PERMISSIVES = frozenset(['force_default_on_freeze',
                                        'force_metaconfig_on_freeze',
                                        'force_store_value'])
 ALLOWED_LEADER_PROPERTIES = frozenset(['empty',
+                                       'notempty',
                                        'notunique',
                                        'unique',
                                        'force_store_value',
diff --git a/tiramisu/value.py b/tiramisu/value.py
index 21e8ccf..e67b7f4 100644
--- a/tiramisu/value.py
+++ b/tiramisu/value.py
@@ -175,7 +175,11 @@ class Values:
                          value,
                          reset_cache=True):
         if isinstance(value, Calculation):
-            value = await value.execute(option_bag)
+            try:
+                value = await value.execute(option_bag)
+            except ConfigError as err:
+                msg = _(f'error when calculating "{option_bag.option.impl_get_display_name()}": {err} : {option_bag.path}')
+                raise ConfigError(msg) from err
         elif isinstance(value, (list, tuple)):
             value = await self._do_value_list(value, option_bag)
         if reset_cache: