fixed check for presence of shielding expressions

src/storm/storage/jani/Property.cpp

@@ -87,7 +87,7 @@ namespace storm {
         }
 
         bool Property::isShieldingProperty() const {
-            return shieldingExpression.is_initialized();
+            return shieldingExpression != boost::none && shieldingExpression.get() != nullptr;
         }
 
         std::shared_ptr<storm::logic::ShieldExpression const> Property::getShieldingExpression() const {

src/storm/storage/jani/Property.h

@@ -156,7 +156,7 @@ namespace storm {
             std::set<storm::expressions::Variable> undefinedConstants;
 
             // TODO might need refactoring, this cannot be expressed by JANI yet, so this is totally wrong here.
-            boost::optional<std::shared_ptr<storm::logic::ShieldExpression const>> shieldingExpression;
+            boost::optional<std::shared_ptr<storm::logic::ShieldExpression const>> shieldingExpression = boost::none;
         };