Events - empty array elements as [] not null

[hwaastad]

Description

Hi,
Currently, if a pull_request has no assignees, the event will have the following:

{
  "event": {
    "pull_request": {
      "assignees": null
    }
  }

I think it would be a better (and more intuitive) way to define arrays as empty [] rather than null (null-safe). This is also more aligned to github events.

Other arrays are:
topics
labels
requested_reviewers
requested_reviewers_teams

Gitea Version

1.23.1

Can you reproduce the bug on the Gitea demo site?

Yes

Log Gist

No response

Screenshots

No response

Git Version

No response

Operating System

No response

How are you running Gitea?

k8s, docker

Database

PostgreSQL