Added appropriate delete statements.

src/dawn/event/Event.hpp

@@ -31,6 +31,8 @@ namespace Dawn {
      * @param callback Callback method that invokes back.
      */
     EventListener(T *instance, void (T::*callback)(A... args)) {
+      assertNotNull(instance);
+
       this->instance = instance;
       this->callback = callback;
     }
@@ -59,7 +61,10 @@ namespace Dawn {
         T *instance,
         void (T::*callback)(A... args)
       ) {
+        assertNotNull(instance);
+
         auto listener = new EventListener<T,A...>(instance, callback);
+        assertNotNull(listener);
         this->listeners.push_back(listener);
         return listener;
       }