The ContextInitializedEvent class represents an event that
should be fired when the context is initialized in order to give registered
listeners time to do proper set up and/or other appropriate actions.
Constucts a ServletInitializedEvent with the specified
servletContextEvent as the nested event.
Parameters: servletContextEvent - the nested servlet context event. throws: NullPointerException - if the specifiedservletContextEvent isnull.