Remove default argument on SessionItem ctor

GUI/Models/SessionItem.h

@@ -205,7 +205,7 @@ class BA_CORE_API_ SessionItem {
 public:
     static const QString P_NAME;
 
-    explicit SessionItem(const QString& modelType = "");
+    explicit SessionItem(const QString& modelType);
     virtual ~SessionItem();
     SessionModel* model() const;
     SessionItem* parent() const;