better error when value not in a choice

tiramisu/error.py

@@ -20,6 +20,8 @@ from .i18n import _
 
 
 def display_list(lst, separator='and', add_quote=False):
+    if not lst:
+        return '""'
     if separator == 'and':
         separator = _('and')
     elif separator == 'or':

tiramisu/option/choiceoption.py

@@ -60,8 +60,8 @@ class ChoiceOption(Option):
         if isinstance(self._choice_values, Calculation):
             values = await self._choice_values.execute(option_bag)
             if values is not undefined and not isinstance(values, list):
-                raise ConfigError(_('calculated values for {0} is not a list'
-                                    '').format(self.impl_getname()))
+                raise ConfigError(_('the calculated values "{0}" for "{1}" is not a list'
+                                    '').format(values, self.impl_getname()))
         else:
             values = self._choice_values
         return values

tiramisu/option/syndynoptiondescription.py

@@ -84,7 +84,8 @@ class SynDynOptionDescription:
 
     async def get_children(self,
                            config_bag: ConfigBag,
-                           dyn: bool=True):
+                           dyn: bool=True,
+                           ):
         subpath = self.impl_getpath()
         children = []
         for child in await self._opt.get_children(config_bag):