we can force mandatory to False

src/rougail/annotator/value.py

@@ -73,7 +73,7 @@ class ValueAnnotator(Walk):  # pylint: disable=R0903
                 if value.type == 'calculation':
                     has_value = False
                     break
-            if has_value:
+            if has_value and 'mandatory' not in vars(variable):
                 # if has value without any calculation
                 variable.mandatory = True
         if not hasattr(variable, 'value'):