Discord.NET中GetUser返回null，无法为用户添加角色

调用await user.AddRoleAsync(role)传入ulong类型的DiscordID时，触发「对象引用未设置到对象实例」错误，确认是user对象为null导致。

我编写了以下测试方法：

private async Task GiveRoleAsync(DiscordSocketClient client, ulong discordId, SocketGuild guild)
{
    try
    {
        if (!string.IsNullOrEmpty(discordId.ToString()) && guild != null)
        {
            Console.WriteLine(discordId);
            var role = guild.Roles.FirstOrDefault(x => x.Name == "Acolyte");
            var roleId = role?.Id;

            if (role != null)
            {
                var user = guild.GetUser(discordId);
                if (user != null)
                {
                        await user.AddRoleAsync(role);
                }
                else
                {
                    Console.WriteLine("User not found in the guild.");
                }
            }
            else
            {
                Console.WriteLine("Role not found.");
            }
        }
        else
        {
            Console.WriteLine("User or Guild ID is null.");
        }
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.ToString());
    }
}

但无论手动传入自己的DiscordID，还是从数据库读取ID传入，都会输出「User not found in the guild.」。Console.WriteLine(discordId)能正常打印出正确的ID，但尝试输出user.Id时会得到null。

我已经启用了Server Members Intent，且通过选择菜单实现的同类功能可以正常运行，对应代码如下：

private async Task GrabRolesHandler(SocketMessageComponent arg)
{
    try
    {
        if (arg.User != null && arg.GuildId != null)
        {
            var text = (arg.Data.Values);
            var userId = arg.User.Id;
            Console.WriteLine(userId);
            SocketGuild guild = _client.GetGuild(arg.GuildId.Value);
            var role = guild.Roles.FirstOrDefault(x => x.Name == text);
            var roleId = role?.Id;
            
            if (role != null)
            {
                var user = guild.GetUser(userId);
                if (user != null)
                {
                    if (user.Roles.Contains(role))
                    {
                        await user.RemoveRoleAsync(role);
                        await arg.RespondAsync($"You have **disabled** pings for the <@&{roleId}> role", ephemeral: true);
                    }
                    else
                    {
                        await user.AddRoleAsync(role);
                        await arg.RespondAsync($"You have **enabled** pings for the <@&{roleId}> role", ephemeral: true);
                    }
                    
                }
                else
                {
                    Console.WriteLine("User not found in the guild.");
                }
            }
            else
            {
                Console.WriteLine("Role not found.");
                await arg.DeferAsync();
            }
        }
        else
        {
            Console.WriteLine("User or Guild ID is null.");
        }
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.ToString());
    }
}

内容的提问来源于stack exchange，提问作者Soggy Meat