avase/8/docs/api/java/lang/IllegalStateException.html?is-external=true" title="class or interface in java.lang" class="externalLink">IllegalStateException</a></code> - if the scope is PageContext.SESSION_SCOPE but the page that was requested does
                                  not participate in a session or the session has been invalidated.</dd>
<dd><code><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/NullPointerException.html?is-external=true" title="class or interface in java.lang" class