[Web Apps] "popup_closed" event contains incorrect payload

[heyqbnk]

Checklist

• [x] I am reporting an issue in existing functionality that does not work as intended
• [x] I've searched for existing GitHub issues

Description

According to official popup_closed documentation, in case no button was clicked, we should receive empty object ({}), but not null.

Expected Behavior

popup_closed event should contain {} payload in case, no button were clicked.

Actual Behavior

popup_closed payload contains null.

Steps to Reproduce

1. Open Web Apps polygon bot (source code)
2. Open developers tools (F12)
3. Call Web Apps method:

bridge.postEvent('web_app_open_popup', {
    title: 'Title',
    message: 'Message',
    buttons: [{type: 'ok', id: 'ok'}]
})

4. Close popup by clicking outside or by clicking popup top right cross
5. See log in console:

[...] [Bridge] [processEvent] popup_closed null

It means, application received event popup_closed with payload presented as null.

Environment

Device: iPhone XR

iOS version: 16.1.1

App version: 9.3.2