Cockpit exception --DefinitionNotFoundException : Language not found for extension zul

I created a custom backoffice extension added to the local extenstion xml. And when I do a hybrisserver start or open any cockpit in browser it throws below exception :

 org.zkoss.zk.ui.metainfo.DefinitionNotFoundException: Language not found for extension zul
     org.zkoss.zk.ui.metainfo.LanguageDefinition.getByExtension(LanguageDefinition.java:194)
     org.zkoss.zk.ui.metainfo.Parser.parse(Parser.java:179)
 

Any idea how to resolve this?