anyone can help me with a respawn script for a zombie?

local time = script.Parent.Parent.respawn_time.Value
while true do
		wait(time)
		local robo=script.Parent:clone()
	robo.Parent = game.Workspace
	robo.HumanoidRootPart.Position = script.Parent.RoboPosition.Position
	robo.Humanoid.WalkSpeed = robo.Parent.WalkSpeed.Value
	robo.Humanoid.MaxHealth = robo.Parent.Health.Value
	
		robo.Script:Destroy()
end

everything looks good I dont knoe why. when i run it it says in the output "Workspace.Robos.Robo.RespawnScript:2: attempt to index nil with 'respawn_time'" even thought it is right