sequence or
          fo:flow and put blocks and inline elements directly as children of
          fo:root or fo:page-sequence, you'll only get a
          NullPointerException. Check whether your FO file has a proper
          structure. In some cases there are mandatory properties, like the
          master-reference in fo:conditional-page-master-reference, check also
          whether you got them right.
        </p>
<p>
          You may find it helpful to use the <a href="#FO-validate">validation tools