code: public ServiceFuture<List<DeletedKeyItem>> getDeletedKeysNextAsync(final String nextPageLink, final ServiceFuture<List<DeletedKeyItem>> serviceFuture, final ListOperationCallback<DeletedKeyItem> serviceCallback) {
          return AzureServiceFuture.fromPageResponse(
              getDeletedKeysNextSinglePageAsync(nextPageLink),
              new Func1<String, Observable<ServiceResponse<Page<DeletedKeyItem>>>>() {
                  @Override
                  public Observable<ServiceResponse<Page<DeletedKeyItem>>> call(String nextPageLink) {
                      return getDeletedKeysNextSinglePageAsync(nextPageLink);
                  }
              },
              serviceCallback);
      }
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.
  @param serviceFuture the ServiceFuture object tracking the Retrofit calls
  @param serviceCallback the async ServiceCallback to handle successful and failed responses.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceFuture} object