lua script help

[Kashian]

Hello,

Need some help with a lua script that keeps giving me a nil value.

Using [redacted] for my macro addon.

function slh()
if buffed("Holy Word: Shield") then cast("Lesser Heal") end
if not buffed("Holy Word: Shield") then cast("Holy Word: Shield") end
end

Basically I want my priest to cast shield on my tank after it fades but if he has shield on than just go straight to casting lesser heal.

I had it working but after casting lesser heal once it stops waiting for shield to come up again instead of going straight to lesser heal.

Any help would be great, Thanks.