Rocket.Chat/server/startup/migrations/v080.js

import { Migrations } from '../../../app/migrations';
import { Integrations } from '../../../app/models';

Migrations.add({
	version: 80,
	up() {
		const query = {
			type: 'webhook-outgoing',
			$or: [{
				channel: [],
			}, {
				channel: '',
			}, {
				channel: {
					$exists: false,
				},
			}],
		};

		const update = {
			$set: {
				channel: ['all_public_channels'],
			},
		};

		Integrations.update(query, update, { multi: true });
	},
});