Properties with type T | undefined can be null

[samildeli]

CommonUserstate from @types/tmi.js (version 1.8.2) has the following type definition:

export interface CommonUserstate {
    badges?: Badges | undefined;
    'badge-info'?: BadgeInfo | undefined;
    color?: string | undefined;
    "display-name"?: string | undefined;
    emotes?: { [emoteid: string]: string[] } | undefined;
    id?: string | undefined;
    mod?: boolean | undefined;
    turbo?: boolean | undefined;
    'emotes-raw'?: string | undefined;
    'badges-raw'?: string | undefined;
    'badge-info-raw'?: string | undefined;
    "room-id"?: string | undefined;
    subscriber?: boolean | undefined;
    'user-type'?: "" | "mod" | "global_mod" | "admin" | "staff" | undefined;
    "user-id"?: string | undefined;
    "tmi-sent-ts"?: string | undefined;
    flags?: string | undefined;
    [paramater: string]: any;
}

When I log the user state like this (tmi.js version 1.8.5):

client.on('message', (channel: string, tags: tmi.ChatUserstate, message: string) => {
    console.log(tags);
  });

We see that the properties with no data are null instead of undefined:

{
  'badge-info': { subscriber: '7' },
  badges: { subscriber: '6', 'glhf-pledge': '1' },
  'client-nonce': 'xxx',
  color: '#FF69B4',
  'display-name': 'xxx',
  emotes: null,
  'first-msg': false,
  flags: null,
  id: 'xxx',
  mod: false,
  'returning-chatter': false,
  'room-id': 'xxx',
  subscriber: false,
  'tmi-sent-ts': '1674488061999',
  turbo: false,
  'user-id': 'xxx',
  'user-type': null,
  'emotes-raw': null,
  'badge-info-raw': null,
  'badges-raw': null,
  username: 'xxx',
  'message-type': 'chat'
}

Also related, I was wondering if it is possible for all properties to be undefined (or null). Do I need to check all of them or only those that are expected to be null?