Fix passing undefined/null handler

[olegbespalov]

What?

Fixes passing undefined/null handler to the addEventListener

Why?

We should not panic.

Checklist

• I have performed a self-review of my code.
• I have added tests for my changes.
• I have run linter locally (make lint) and all checks pass.
• I have run tests locally (make test) and all tests pass.
• I have commented on my code, particularly in hard-to-understand areas.

Related PR(s)/Issue(s)