code: @Nonnull
    public AS2ClientBuilder setAS2ClientFactory (@Nonnull final ISupplier <AS2Client> aAS2ClientFactory)
    {
      m_aAS2ClientFactory = ValueEnforcer.notNull (aAS2ClientFactory, "AS2ClientFactory");
      return this;
    }
docs: Set the factory to create {@link AS2Client} objects internally. Overwrite
  this if you need a proxy in the AS2Client object. By default a new instance
  of AS2Client is created so you don't need to call this method.
  
  @param aAS2ClientFactory
  The factory to be used. May not be <code>null</code>.
  @return this for chaining