Follow the steps described in ZKSPRING-20, including the fix.

In CoreContextListener, preprocessSpringBeansForZKComponentinjection:

The method call sce.getServletContext().getRealPath("/WEB-INF/classes") returns null.
The null value is later passed on to the call: mainClass.writeFile(webInf);

The result is that the ZKComponentBeanMethods.class is written to the directory

DOMAIN-DIR/null/org/zkoss/spring/beans/zkcomponents