public Optional<IQ> processNoSuchUserCheck(final IQ stanza)
    {
        // Use the detection mechanism as implemented by the superclass, but use our own result stanza.
        if (super.processNoSuchUserCheck(stanza).isPresent()) {
            final IQ response = IQ.createResultIQ(stanza);
            response.setChildElement(stanza.getChildElement().createCopy());
            return Optional.of(response);
        }
        return Optional.empty();
    }
XEP-0030 Section 8 contradict RFC 6121 8.5.1. "No Such User" in its definition on how the server must
respond to a request made against a non-existing user. This method overrides the default implementation of
RFC 6121's definition (from the super class) with that of XEP-0030:

<blockquote>The following rules apply to the handling of service discovery requests sent to bare JIDs: [...] In
response to a disco#items request, the server MUST return an empty result set if: [...] The target entity does
not exist (no matter if the request specifies a node or not).</blockquote>

@see <a href="https://xmpp.org/extensions/xep-0030.html#security">XEP-0030 8 "Security Considerations"</a>
@see <a href="https://xmpp.org/rfcs/rfc6121.html#rules-localpart-nosuchuser">RFC 6121 8.5.1. "No Such User"</a>
@see <a href="https://igniterealtime.atlassian.net/jira/software/c/projects/OF/issues/OF-880">OF-880</a>
xmppserver/src/main/java/org/jivesoftware/openfire/disco/IQDiscoItemsHandler.java