minor fix

hrt/prefab/l3d/Level3D.hx

@@ -29,6 +29,7 @@ class Level3D extends hrt.prefab.Library {
 	#if editor
 
 	override function getCdbModel(?p:hrt.prefab.Prefab) : cdb.Sheet {
+		if( p == null ) p = this;
 		return @:privateAccess hide.view.l3d.Level3D.getCdbModel(p);
 	}