Use NULL for memory addresses

engine/SceneGraph.cpp

@@ -43,7 +43,7 @@ SceneGraph::SceneGraph(Allocator& a, uint32_t index)
 	: m_allocator(&a)
 	, m_index(index)
 	, m_num_nodes(0)
-	, m_flags(0)
+	, m_flags(NULL)
 	, m_world_poses(NULL)
 	, m_local_poses(NULL)
 	, m_parents(NULL)