Fix invalid study after update to v8.7.0 - Add default group to exist…

…ing BCs (#1462)

* [UPDATER] Fix invalid study after update to v8.7.0

- Starting from v8.7.0, all binding constraints should have a 'group'
    attribute with a non-empty group
- Before this change, the updater produced wrong constraints

* Use group "default" instead of "legacy_study_group"

src/libs/antares/study/binding_constraint/BindingConstraintLoader.cpp

@@ -160,9 +160,9 @@ std::vector<std::shared_ptr<BindingConstraint>> BindingConstraintLoader::load(En
                          << "]: Missing mandatory binding constraint group";
             return {};
         }
-        else
+        else // In studies versions < 870, binding constraints have no group. From version 870, antares requires constraints to have a group.
         {
-            bc->group_ = "legacy_study_group";
+            bc->group_ = "default";
         }
     }
 

src/libs/antares/study/binding_constraint/BindingConstraintSaver.cpp

@@ -21,6 +21,9 @@ bool BindingConstraintSaver::saveToEnv(EnvForSaving& env, const BindingConstrain
     env.section->add("filter-year-by-year", datePrecisionIntoString(bindingConstraint->pFilterYearByYear));
     env.section->add("filter-synthesis", datePrecisionIntoString(bindingConstraint->pFilterSynthesis));
 
+    if (!bindingConstraint->group().empty())
+        env.section->add("group", bindingConstraint->group());
+
     if (!bindingConstraint->pComments.empty())
         env.section->add("comments", bindingConstraint->pComments);