code: void checkImageManagers() throws IOException {
      updateImageMetrics();
      int numAvailable = 0;
      for (ImageManager im : imageManagers) {
        if (!im.isImageDisabled()) {
          numAvailable++;
        }
      }
      if (numAvailable == 0) {
        throwIOException("No image locations are available");
      }
    }
docs: Check if any image managers are available.