Don't allow Event with null parameters
Don't allow Event with null parameters

Change Event to not allow to set null parameters, to avoid consumers to
check for null.

Related to zaproxy/zap-extensions#1798 - websocket: fix NPE when
dispatching events

meitar/zaproxy,zaproxy/zaproxy,meitar/zaproxy,zapbot/zaproxy,gmaran23/zaproxy,psiinon/zaproxy,zapbot/zaproxy,kingthorin/zaproxy,zaproxy/zaproxy,zapbot/zaproxy,psiinon/zaproxy,meitar/zaproxy,psiinon/zaproxy,kingthorin/zaproxy,zaproxy/zaproxy,zaproxy/zaproxy,thc202/zaproxy,zaproxy/zaproxy,thc202/zaproxy,thc202/zaproxy,meitar/zaproxy,thc202/zaproxy,Ali-Razmjoo/zaproxy,zapbot/zaproxy,zaproxy/zaproxy,Ali-Razmjoo/zaproxy,kingthorin/zaproxy,gmaran23/zaproxy,zapbot/zaproxy,meitar/zaproxy,thc202/zaproxy,kingthorin/zaproxy,zapbot/zaproxy,gmaran23/zaproxy,psiinon/zaproxy,zapbot/zaproxy,gmaran23/zaproxy,Ali-Razmjoo/zaproxy,meitar/zaproxy,psiinon/zaproxy,psiinon/zaproxy,Ali-Razmjoo/zaproxy,zaproxy/zaproxy,thc202/zaproxy,Ali-Razmjoo/zaproxy,meitar/zaproxy,gmaran23/zaproxy,kingthorin/zaproxy,meitar/zaproxy,kingthorin/zaproxy,gmaran23/zaproxy,gmaran23/zaproxy,Ali-Razmjoo/zaproxy,psiinon/zaproxy,thc202/zaproxy,Ali-Razmjoo/zaproxy,kingthorin/zaproxy