I d'like to setup only a session mail factory (no mimepart)

I add in my easybeans.xml
<mail>
   <session name="javax.mail.Session" jndiName="MailSession">
      <!-- Example of properties -->
      <property name="mail.debug" value="true" />
   </session>
</mail>

And I got an NPE, until I add mimepart factory

    /**
     * @return list of factories.
     */
    public List<MailItf> getAllFactories() {
        List<MailItf> factories = new ArrayList<MailItf>();
        factories.addAll(sessionFactories);
        factories.addAll(mimePartFactories);
        return factories;
    }

but mimePartFactories is null so I got an NPE.

Thx