code: public Observable<Page<DeletedKeyItem>> getDeletedKeysNextAsync(final String nextPageLink) {
          return getDeletedKeysNextWithServiceResponseAsync(nextPageLink)
              .map(new Func1<ServiceResponse<Page<DeletedKeyItem>>, Page<DeletedKeyItem>>() {
                  @Override
                  public Page<DeletedKeyItem> call(ServiceResponse<Page<DeletedKeyItem>> response) {
                      return response.body();
                  }
              });
      }
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 observable to the PagedList&lt;DeletedKeyItem&gt; object