Fix 'prevent-addEventListener' - scriptlet throws error when 'null' is used as event type

[AdamWr]

Steps to reproduce:

1. Add to user rules:

adguard.com#%#//scriptlet('prevent-addEventListener', 'testEvent')

2. Navigate to - https://adguard.com/
3. Open console and run:

console.log('Start');
document.addEventListener(null, ()=>{});
console.log('End');

It should print Start and End.
Currently it prints Start only, because addEventListener throws error when null is used as a type.