code: public static void handleCause(final ExecutionException ex)
              throws ConcurrentException {
          final ConcurrentException cex = extractCause(ex);
  
          if (cex != null) {
              throw cex;
          }
      }
docs: Handles the specified {@code ExecutionException}. This method calls
  {@link #extractCause(ExecutionException)} for obtaining the cause of the
  exception - which might already cause an unchecked exception or an error
  being thrown. If the cause is a checked exception however, it is wrapped
  in a {@code ConcurrentException}, which is thrown. If the passed in
  exception is <b>null</b> or has no cause, the method simply returns
  without throwing an exception.
  
  @param ex the exception to be handled
  @throws ConcurrentException if the cause of the {@code
  ExecutionException} is a checked exception