schema is not mandatory

tiramisu_api/api.py

@@ -225,13 +225,14 @@ class _Value:
              withwarning: bool=False,
              flatten: bool=False):
         ret = {}
-        self._dict_walk(ret,
-                        self.schema,
-                        self.path,
-                        fullpath,
-                        withwarning,
-                        flatten,
-                        None)
+        if self.schema:
+            self._dict_walk(ret,
+                            self.schema,
+                            self.path,
+                            fullpath,
+                            withwarning,
+                            flatten,
+                            None)
         return ret
 
 
@@ -609,9 +610,12 @@ class ContextValue(_Value):
                  config: 'Config',
                  schema: Dict) -> None:
         self.config = config
-        first = next(iter(schema.keys()))
-        self.path = first.rsplit('.', 1)[0]
-        self.schema = {'properties': schema}
+        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,