code: protected FetchException transformIntoFetchException(Throwable e) {
          if (e instanceof FetchException) {
              return (FetchException) e;
          }
          if (e instanceof InterruptedIOException ||
              e instanceof ClosedByInterruptException) {
              return new FetchInterruptedException(e);
          }
          return null;
      }
docs: Override to support custom transformations, returning null if none is
  applicable. Be sure to call super first. If it returns non-null, return
  that result.
  
  @param e required exception to transform
  @return FetchException, or null if no applicable transform