code: public static CompletionException asCompletionException( Throwable error )
      {
          if ( error instanceof CompletionException )
          {
              return ((CompletionException) error);
          }
          return new CompletionException( error );
      }
docs: Helped method to turn given exception into a {@link CompletionException}.
  
  @param error the exception to convert.
  @return given exception wrapped with {@link CompletionException} if it's not one already.