code: private static BoxRetentionPolicy.Info createRetentionPolicy(BoxAPIConnection api, String name, String type,
                                                                  int length, String action) {
          return createRetentionPolicy(api, name, type, length, action, null);
      }
docs: Used to create a new retention policy.
  @param api the API connection to be used by the created user.
  @param name the name of the retention policy.
  @param type the type of the retention policy. Can be "finite" or "indefinite".
  @param length the duration in days that the retention policy will be active for after being assigned to content.
  @param action the disposition action can be "permanently_delete" or "remove_retention".
  @return the created retention policy's info.