Steps to Reproduce

try to change the current theme with websockets enabled

<button onClick='Themes.setTheme(Executions.getCurrent(),"breeze");'/>

and calling getCurrentTheme doesn't resolve the current theme based on an existing cookie, the list of cookies is empty (in: org.zkoss.zul.theme.CookieThemeResolver#getTheme)

String currentTheme = Themes.getCurrentTheme();

Current Result

java.lang.NullPointerException
	at org.zkoss.zul.theme.CookieThemeResolver.setTheme(CookieThemeResolver.java:73)
	at org.zkoss.zul.theme.Themes.setTheme(Themes.java:71)

Expected Result

no exception

Root Cause

websocket connections don't have cookies

Workaround

setting the cookie manually:

String contextPath = Executions.getCurrent().getContextPath();
Clients.evalJavaScript(String.format("document.cookie = 'zktheme=%s;path=%s';", "breeze", contextPath));