What does "attempt to index nil with 'FindFirstChild'" mean?

I am making a tycoon with GamerM8' videos, and I am pretty sure I have copied the script word for word, I have messed around with dependency and item StringValues and it still comes up with an error: "Workspace.Tycoon Model.Scripts.MainScript:27: attempt to index nil with 'FindFirstChild'"

Code:

--- Buying Functions ---

for i,v in pairs(Buttons:GetChildren()) do local NewItem = BoughtItems:FindFirstChild(v.Item.Value) if NewItem ~= nil then Items[NewItem.Name] = NewItem:Clone() NewItem:Destroy() else v.ButtonPart.Transparency = 1 v.ButtonPart.CanCollide = false end

if v:FindFirstChild("Dependency") then
    coroutine.resume(coroutine.create(function()
        v.ButtonPart.Transparency = 1
        v.ButtonPart.CanCollide = false
        if BoughtItems:WaitForChild(v.Dependency.Value, 100000) then
            v.ButtonPart.Transparency = 0
            v.ButtonPart.CanCollide = true
        end
    end))
end

v.ButtonPart.Touched:Connect(function(Hit)
    if Hit.Parent:FindFirstChild("Humanoid") then
        local Player = game.Players:GetPlayerFromCharacter(Hit.Parent)
        if Values.OwnerValue.Value == Player then
            if v.ButtonPart.CanCollide == true and v.ButtonPart.Transparency == 0 then
                if Player:WaitForChild("leaderstats").Cash.Value >= v.Price.Value then
                    Player.leaderstats.Cash.Value -= v.Price.Value
                    Items[v.Item.Value].Parent = BoughtItems
                    v:Destroy()
                end
            end
        end
    end
end)

end

the line in question would be: local NewItem = BoughtItems:FindFirstChild(v.Item.Value)