- protected var child0: nullable QuadTree[E]
- protected var child1: nullable QuadTree[E]
- protected var child2: nullable QuadTree[E]
- protected var child3: nullable QuadTree[E]
+ protected var child0: nullable QuadTree[E] = null
+ protected var child1: nullable QuadTree[E] = null
+ protected var child2: nullable QuadTree[E] = null
+ protected var child3: nullable QuadTree[E] = null