HTTP requests breaking?

I'm using the twitch api to pull information about a channel. When I put in a valid channel it works, but after I put in a non-valid channel, it stops working. Any ideas why and how to fix it?

function handle(err)
errortext = 'ERROR: ' .. err:gsub("(.-:)","")
	return errortext
end

function pcallgetasync(person)
getasync = game:GetService('HttpService'):GetAsync('https://api.twitch.tv/kraken/channels/' .. person, true)
return getasync
end



game.Players.PlayerAdded:connect(function(player)
	player.PlayerGui:WaitForChild('ScreenGui').Frame.SearchBox.Search.Changed:connect(function()
		person = player.PlayerGui.ScreenGui.Frame.SearchBox.Text
		if player.PlayerGui:WaitForChild('ScreenGui').Frame.SearchBox.Search.Value == true then
			local httpservice = game:GetService('HttpService')
			player.PlayerGui.ScreenGui.Frame.SearchBox.Changed:connect(function()
				person = player.PlayerGui.ScreenGui.Frame.SearchBox.Text
			end)
			if pcall (function() pcallgetasync(person) end) then
				afollowers = string.find(getasync, '"followers":')
				endthing = string.find(getasync, ',"_links"')
				followers = string.sub(getasync, afollowers + 12, endthing - 1)
				player.PlayerGui.ScreenGui.Frame.Followers.Text = 'Followers: ' .. followers
				player.PlayerGui.ScreenGui.Frame.SearchBox.Search.Value = false
			else
				print(xpcall(pcallgetasync, handle))
				--errortext = tostring(xpcall(pcallgetasync, handle))
				a = require(game.Workspace.ErrorScript)
				a(player.Name, errortext)
			end
		end
	end)
end)

(I have not tested this so I cannot guarantee that this is the only issue)

Line 21 checks that you are able to get a response. However, it does not guarantee that your response is in the form you expected.

You search for '"followers":' and ',"_links"'; however, if the string does not contain those, then that search will result in nil.

In the following line, you operate on (adding / substring, and using as arguments to string.sub) afollowers and endthing even though they could be nil, which will cause an error.

You should check that they have values:

if afollowers and endthing then

and only then proceed.