Attempt to index nil with character?

I was running my code, and I got an error called "attempt to index nil with character. Can someone explain what this means?

local Door1 = script.Parent.Door1
local Door2 = script.Parent.Door2
local player = game.Players.LocalPlayer
local character = player.Character or player.CharacterAdded:wait()
local neon = script.Parent.Button.Neon
local neonb = script.Parent.Button2.Neon2
local debounce = false
local opened = false -- new variable
local TS = game:GetService("TweenService")
local TI = TweenInfo.new(0.8, Enum.EasingStyle.Linear, Enum.EasingDirection.Out, 0, false, 0)
local DoorOpen1 = {CFrame = Door1.CFrame + Door1.CFrame.lookVector * -4}
local DoorOpen2 = {CFrame = Door2.CFrame + Door2.CFrame.lookVector * 4}
local DoorClose1 = {CFrame = Door1.CFrame }
local DoorClose2 = {CFrame = Door2.CFrame }
local open1 = TS:Create(Door1, TI, DoorOpen1)
local close1 = TS:Create(Door1, TI, DoorClose1)
local open2 = TS:Create(Door2, TI, DoorOpen2)
local close2 = TS:Create(Door2, TI, DoorClose2)
local sound = script.Parent["BMRF Sliding Door Open"]
local closesound = script.Parent["BMRF Sliding Door Close"]

script.Parent.Parent.ToggleDoor.OnServerEvent:Connect(function()
    if player.Backpack:FindFirstChild("card") or player.Character:FindFirstChild("card") then 
        if opened == false then -- is it OPEN...?
            if debounce == false then -- then check debounce
                debounce = true
                opened = true
                neon.BrickColor = BrickColor.new("Bright green")
                neonb.BrickColor = BrickColor.new("Bright green")
                sound:Play()
                open1:Play()
                open2:Play()
                wait(1) -- wait a bit (optional)
                debounce = false -- reset the debounce
            end
        elseif opened == true then
            if debounce == false then -- same thing as above
                debounce = true
                opened = false
                neon.BrickColor = BrickColor.new("Really red")
                neonb.BrickColor = BrickColor.new("Really red")
                closesound:Play()
                close1:Play()
                close2:Play()
                wait(1)
                debounce = false
            end
        end
    end
end)