public BufferedImage getSprite(String key) throws NullPointerException {
        if (VectorWorld.DEBUG_GFX) {
            System.out.println("Trying to get the sprite with key "
                    + key + "...");
        }
        BufferedImage bi = (BufferedImage) imagesMap.get(key);
        if (bi == null) {
            if(VectorWorld.DEBUG_GFX) {
                System.err.println("Failed to get the sprite.");
            }
            throw new NullPointerException("No image for key: " + key);
        } else  if(VectorWorld.DEBUG_GFX) {
            System.out.println("Got the sprite.");
        }
        return bi;
    }