Attempt to index nil with 'FindFirstChildOfClass'

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#1

I’m trying to make a spawn car script, where if a player pressed the button it has to decide between 2 options, Spawn a basic car Or spawn an advanced car. But I get an error stating that It attempted to index nil with function :FindFirstChildOfClass()

local localplayer = game.Players.LocalPlayer

local b = script.Parent.spawncar

local seat = true

b.MouseButton1Click:Connect(function()
	 a = localplayer.PlayerGui.CarGui:WaitForChild("firstSeat")
	 b = localplayer.PlayerGui.CarGui:WaitForChild("secondSeat")
	
	if seat then
		a.Visible = true
		b.Visible = true
	else
		a.Visible = false
		b.Visible = false
	end
end)

a:FindFirstChildOfClass("TextButton").MouseButton1Click:Connect(function()
	game.ReplicatedStorage.something:FireServer(false)
end)

b:FindFirstChildOfClass("TextButton").MouseButton1Click:Connect(function()
	game.ReplicatedStorage.something:FireServer(true)
end)
#2

A isn’t defined in the top-most local block

#3 
local replicated = game:GetService("ReplicatedStorage")
local something = replicated:WaitForChild("Something")

local players = game:GetService("Players")
local player = players.LocalPlayer
local playergui = player:WaitForChild("PlayerGui")
local cargui = playergui:WaitForChild("CarGui")
local first = cargui:WaitForChild("firstSeat")
local second = cargui:WaitForChild("secondSeat")
local firstButton = first:WaitForChild("TextButton")
local secondButton = second:WaitForChild("TextButton")
local parent = script.Parent
local spawncar = parent:WaitForChild("spawncar")

local seat = true

spawncar.MouseButton1Click:Connect(function()
	if seat then
		seat = false
		first.Visible = true
		second.Visible = true
	else
		seat = true
		first.Visible = false
		second.Visible = false
	end
end)

firstButton.MouseButton1Click:Connect(function()
	something:FireServer(false)
end)

secondButton.MouseButton1Click:Connect(function()
	something:FireServer(true)
end)

I tried.