docs: @Pure
  	public QuadTreeZone zoneOf(N child) {
  		if (child == this.nNorthWest) {
  			return QuadTreeZone.NORTH_WEST;
  		}
  		if (child == this.nNorthEast) {
  			return QuadTreeZone.NORTH_EAST;
  		}
  		if (child == this.nSouthWest) {
  			return QuadTreeZone.SOUTH_WEST;
  		}
  		if (child == this.nSouthEast) {
  			return QuadTreeZone.SOUTH_EAST;
  		}
  		return null;
  	}