code: public Observable<ServiceResponse<Page<DeletedKeyItem>>> getDeletedKeysNextSinglePageAsync(final String nextPageLink) {
          if (nextPageLink == null) {
              throw new IllegalArgumentException("Parameter nextPageLink is required and cannot be null.");
          }
          String nextUrl = String.format("%s", nextPageLink);
          return service.getDeletedKeysNext(nextUrl, this.acceptLanguage(), this.userAgent())
              .flatMap(new Func1<Response<ResponseBody>, Observable<ServiceResponse<Page<DeletedKeyItem>>>>() {
                  @Override
                  public Observable<ServiceResponse<Page<DeletedKeyItem>>> call(Response<ResponseBody> response) {
                      try {
                          ServiceResponse<PageImpl<DeletedKeyItem>> result = getDeletedKeysNextDelegate(response);
                          return Observable.just(new ServiceResponse<Page<DeletedKeyItem>>(result.body(), result.response()));
                      } catch (Throwable t) {
                          return Observable.error(t);
                      }
                  }
              });
      }
docs: Lists the deleted keys in the specified vault.
  Retrieves a list of the keys in the Key Vault as JSON Web Key structures that contain the public part of a deleted key. This operation includes deletion-specific information. The Get Deleted Keys operation is applicable for vaults enabled for soft-delete. While the operation can be invoked on any vault, it will return an error if invoked on a non soft-delete enabled vault. This operation requires the keys/list permission.
  
  @param nextPageLink The NextLink from the previous successful call to List operation.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the PagedList&lt;DeletedKeyItem&gt; object wrapped in {@link ServiceResponse} if successful.