Attempt to index nil with "FindFirstChild"?

I am making a localscript that is supposed to make the screen read on death, but when I try to check HealthChanged, it gives me this error.

Players.Uniplier.PlayerGui.Death.Death:3: attempt to index nil with 'FindFirstChild'

Here is my code.

local player = game:GetService("Players").LocalPlayer 
local char = player:FindFirstChild("Character")
char:FindFirstChild("Humanoid").HealthChanged:Connect(function()
    if char.charactervalues.Grabbed.Value == true then
        local death = script.Parent.Frame
        if char.Humanoid.Health <= 1 then
            death.Transparency = 0
        end
    end
end)