class WallHolderService implements WallDAO {

    @Override
    public Wall find(String wallName) throws NotFoundException {
        Preconditions.checkNotNull(wallName, "wallName");
        Wall wall = WALLS.get(wallName);
        if (wall == null) {
            throw new NotFoundException("Wall with name : " + wallName + " not found");
        }
        return wall;
    }

}