code: @Nonnull
    public ESuccess writeTo (@Nonnull @WillClose final OutputStream aOS)
    {
      try
      {
        ValueEnforcer.notNull (aOS, "OutputStream");
  
        if (m_nCreatedCellStyles > 0 && LOGGER.isDebugEnabled ())
          LOGGER.debug ("Writing Excel workbook with " + m_nCreatedCellStyles + " different cell styles");
  
        m_aWB.write (aOS);
        return ESuccess.SUCCESS;
      }
      catch (final IOException ex)
      {
        if (!StreamHelper.isKnownEOFException (ex))
          LOGGER.error ("Failed to write Excel workbook to output stream " + aOS, ex);
        return ESuccess.FAILURE;
      }
      finally
      {
        StreamHelper.close (aOS);
      }
    }
docs: Write the current workbook to an output stream.
  
  @param aOS
  The output stream to write to. May not be <code>null</code>. Is
  automatically closed independent of the success state.
  @return {@link ESuccess}