schema is not mandatory

tiramisu_api/api.py

@@ -225,6 +225,7 @@ class _Value:
              withwarning: bool=False,
              flatten: bool=False):
         ret = {}
+        if self.schema:
             self._dict_walk(ret,
                             self.schema,
                             self.path,
@@ -609,9 +610,12 @@ class ContextValue(_Value):
                  config: 'Config',
                  schema: Dict) -> None:
         self.config = config
+        if schema:
             first = next(iter(schema.keys()))
             self.path = first.rsplit('.', 1)[0]
             self.schema = {'properties': schema}
+        else:
+            self.schema = {}
 
     def __call__(self) -> TiramisuOptionValue:
         return TiramisuOptionValue(self.config,