找不到用户 Discord.net

Question

我做了一个应该禁止人们的命令，但是当我编写该命令时，它说“找不到用户”，即使他在服务器中，这是代码：

        [Command("ban")]
    [RequireUserPermission(GuildPermission.BanMembers, ErrorMessage ="You don't have the permission ``ban_member``!")]
    public async Task BanMember(IGuildUser user = null, [Remainder] string reason = null)
    {
        if (user == null)
        {
            await ReplyAsync("Please specify a user!"); 
            return;
        }
        if (reason == null) reason = "Not specified";

        await Context.Guild.AddBanAsync(user, 1, reason);

        var EmbedBuilder = new EmbedBuilder()
            .WithDescription($":white_check_mark: {user.Mention} was banned\n**Reason** {reason}")
            .WithFooter(footer =>
            {
                footer
                .WithText("User Ban Log")
                .WithIconUrl("https://i.imgur.com/6Bi17B3.png");
            });
        Embed embed = EmbedBuilder.Build();
        await ReplyAsync(embed: embed);

        ITextChannel logChannel = Context.Client.GetChannel(id) as ITextChannel;
        var EmbedBuilderLog = new EmbedBuilder()
            .WithDescription($"{user.Mention} was banned\n**Reason** {reason}\n**Moderator** {Context.User.Mention}")
            .WithFooter(footer =>
            {
                footer
                .WithText("User Ban Log")
                .WithIconUrl("https://i.imgur.com/6Bi17B3.png");
            });
        Embed embedLog = EmbedBuilderLog.Build();
        await logChannel.SendMessageAsync(embed: embedLog);

    }