How can I check if my "variable" is a valid "ID"

Question

API: https://github.com/satom99/litcord

How can I check my valiable if its a valid ID?

local cmd, serverID, channelID, arg = string.match(message.content, '(%S+) (%d+) (%d+) (%S+.*)')    
local server = client.servers:get('id', serverID)

serverID is the variable and I need to check if the serverID is a valid ID Otherwise I will get an error that server is a nil value.

I am trying days to finish one command and this is a part of it. If you need more contents then please tell me, I will link it to you.

Full Code:

client:on(
    'message',
    function(message)
      local userID = message.author.id
      local cmd, serverID, channelID, arg = string.match(message.content, '(%S+) (%d+) (%d+) (%S+.*)')
      local server = client.servers:get('id', serverID)
      local channel = server.channels:get('id', channelID)
      local cmd = cmd or message.content
      if (cmd == "!say") and message.parent.is_private then 
        if (userID == "187590758360940545") then

          if not server then
            return
          end

          if (server == servers) then

            if (channel == channels) then
              message.channel:sendMessage(arg)
            else
              message:reply("I don't know this channel.")
              return
            end

            message:reply("I don't know this server.")

          end

        else
          message:reply(":sob: Stop!!!!")
        end
      end
    end
)

And how I can let it write in the channel I want with functions message.channel:sendMessage(arg) this is like message:reply it replies back where the message came from.

Answer 1

Let's forget about validating the serverID for one moment.

Of course you should always handle the case client.servers:get('id', serverID) returing nil.

Simply validating serverID somehow and hoping that you will get a valid server handle back is not an option.

So either use Luas error handling features https://www.lua.org/manual/5.3/manual.html#2.3

or simply check server with an if statement so you won't use server if it is nil.

Simplified:

local server = client.servers:get('id', serverID)
if not server then
  print("No server with id '" .. serverID .. "' found.")
  return -- or do something clever here, show a message box or whatever...
end
-- server won't be nil from here

Unless you know for sure that there is no other way for nil being returned you should handle that possibility properly.