setMentionedUsers method
Implementation
void setMentionedUsers(List<User> mentionedUsers) {
  for (var user in mentionedUsers) {
    String key = "@${user.name}";
    if (mentionedUsersMap.containsKey(key)) {
      mentionedUsersMap[key]!.add(user);
    } else {
      mentionedUsersMap[key] = [user];
    }
  }
}