code: @Override
    public Volumes getAvailableVolumes(String regionSlug)
        throws DigitalOceanException, RequestUnsuccessfulException {
      checkBlankAndThrowError(regionSlug, "Missing required parameter - regionSlug.");
  
      Map<String, String> data = new HashMap<String, String>();
      data.put("region", regionSlug);
      return (Volumes) perform(new ApiRequest(ApiAction.AVAILABLE_VOLUMES, data)).getData();
    }
docs: =======================================