Problem with webhooks and the role/permissions idea - discord

Question

I develop a bot with discord.js that uses things like msg.member.hasPermission("ADMINISTRATOR") or msg.member.roles.cache.has(teacherRoleID). Everything worked fine until I tried webhooks. By adding these two lines :
client.on('ready', () => {
client.user.setStatus("online")
client.user.setActivity("!help", {
type: "PLAYING",
});
superConsole(`Logged in as ${client.user.tag} in ${client.guilds.size} guilds!`);
const hook = new Discord.WebhookClient("ID", "secret token"); // THESE
hook.send("I am now alive!"); // LINES
});
(btw superConsole is a function)
Since then, the program did not work any more and always returned the same errors: (node:20736) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'hasPermission' of null & (node:20736) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'roles' of null
When I delete these 2 lines for the webhook, it works again. Why? I don't understand.
The permission and role things are in a message listener:
client.on('message', async msg => {
if (msg.member.hasPermission('ADMINISTRATOR') {
// some stuff here
}
if (msg.member.roles.cache.has(teacherRoleID) {
// some stuff here
}
});

Answer 1

The issue is that when you send a message from hook, it triggers the client's message event. Because a webhook isn't a guild member, msg.member will get undefined for messages sent from a webhook.
You would have to use something like this:
if (msg.member) {
if (msg.member.permissions.has('ADMINISTRATOR') {
// some stuff here
}
if (msg.member.roles.cache.has(teacherRoleID) {
// some stuff here
}
}