Buff Timer to be Statusbar instead of text

[Joker119]

I'm sorry but I'm missing something crucial here..
I'm trying to impliment a similar feature into my UI addon, but

            local _, _, _, _, _, duration, expirationTime = UnitAura(PlayerFrame.unit, index, filter)
            if duration > 0 and expirationTime then
                  -- This aura has a duration:
                  BuffStatusBar:SetMinMaxValues(expirationTime - duration, expirationTime)
            else
                  -- This aura doesn't have a duration:
                  BuffStatusBar:SetMinMaxValues(0, 1)
                  BuffStatusBar:SetValue(1)
            end

gives me an error saying

 if duration > 0 and expirationTime then

is trying to compare a number to a nil.

I have everything else working except this.