code: protected RepositoryException transformIntoRepositoryException(Throwable e) {
          if (e instanceof RepositoryException) {
              return (RepositoryException) e;
          }
          RepositoryException re = transformIntoFetchException(e);
          if (re != null) {
              return re;
          }
          re = transformIntoPersistException(e);
          if (re != null) {
              return re;
          }
          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 RepositoryException, or null if no applicable transform