StanzasErrorException is not triggered

[rheman]

Hi everyone.
I am using the library for managing my ejabberd user. But https://xmpp.org/extensions/xep-0086.html seems to be deprecated and was rolled into the new [xmpp-core] http://xmpp.org/rfcs/rfc6120.html. Stanza errors are defined in https://xmpp.org/rfcs/rfc6120.html#stanzas-error and https://xmpp.org/rfcs/rfc3920.html#rfc.section.9.3.3.
So when try to register a user throuh fabiang library everything works perferctly. But when I try to register one more time and existing user the StanzasErrorException is not trigger.
Could someone help me ?
I dont know what's wrong with my settings.
Best ragard.