Esse é o erro que aparece no meu console:

Lua Script Error: [Action Interface] 
data/actions/scripts/other/strengthening_potions.lua:onUse 
data/actions/scripts/other/strengthening_potions.lua:30: attempt to call method 'isMage' (a nil value) 
stack traceback: 
[C]: in function 'isMage' 
data/actions/scripts/other/strengthening_potions.lua:30: in function 

aqui está o script:

local berserker = Condition(CONDITION_ATTRIBUTES)
berserker:setParameter(CONDITION_PARAM_TICKS, 10 * 60 * 1000)
berserker:setParameter(CONDITION_PARAM_SKILL_MELEE, 5)
berserker:setParameter(CONDITION_PARAM_SKILL_SHIELD, -10)

local mastermind = Condition(CONDITION_ATTRIBUTES)
mastermind:setParameter(CONDITION_PARAM_TICKS, 10 * 60 * 1000)
mastermind:setParameter(CONDITION_PARAM_STAT_MAGICPOINTS, 3)
mastermind:setParameter(CONDITION_PARAM_SKILL_SHIELD, -10)

local bullseye = Condition(CONDITION_ATTRIBUTES)
bullseye:setParameter(CONDITION_PARAM_TICKS, 30 * 60 * 1000)
bullseye:setParameter(CONDITION_PARAM_SKILL_DISTANCE, 5)
bullseye:setParameter(CONDITION_PARAM_SKILL_SHIELD, -10)

local config = {
	[7439] = berserker,
	[7440] = mastermind,
	[7443] = bullseye
}

function onUse(cid, item, fromPosition, itemEx, toPosition)
	local useItem = config[item.itemid]
	if not useItem then
		return true
	end

	local player = Player(cid)
	if item.itemid == 7440 then
		if not player:isMage() then
			doPlayerSendTextMessage(cid,18,'Only sorcerers and druids may drink this fluid.', TALKTYPE_MONSTER_SAY)
			return true
		end
	end

	local cStorage = player:getStorageValue(Storage.Achievements.PotionAddict)
	if cStorage < 100000 then
		player:setStorageValue(Storage.Achievements.PotionAddict, math.max(1, cStorage) + 1)
	elseif cStorage == 100000 then
		player:addAchievement('Potion Addict')
		player:setStorageValue(Storage.Achievements.PotionAddict, 100001)
	end

	player:addCondition(useItem)
	player:getPosition():sendMagicEffect(CONST_ME_MAGIC_RED)
	Item(item.uid):remove(1)
	return true
end

alguem poderia ajudar?

Testa ai:

local berserker = Condition(CONDITION_ATTRIBUTES)
berserker:setParameter(CONDITION_PARAM_TICKS, 10 * 60 * 1000)
berserker:setParameter(CONDITION_PARAM_SKILL_MELEE, 5)
berserker:setParameter(CONDITION_PARAM_SKILL_SHIELD, -10)

local mastermind = Condition(CONDITION_ATTRIBUTES)
mastermind:setParameter(CONDITION_PARAM_TICKS, 10 * 60 * 1000)
mastermind:setParameter(CONDITION_PARAM_STAT_MAGICPOINTS, 3)
mastermind:setParameter(CONDITION_PARAM_SKILL_SHIELD, -10)

local bullseye = Condition(CONDITION_ATTRIBUTES)
bullseye:setParameter(CONDITION_PARAM_TICKS, 30 * 60 * 1000)
bullseye:setParameter(CONDITION_PARAM_SKILL_DISTANCE, 5)
bullseye:setParameter(CONDITION_PARAM_SKILL_SHIELD, -10)

local config = {
    [7439] = berserker,
    [7440] = mastermind,
    [7443] = bullseye
}

function onUse(cid, item, fromPosition, itemEx, toPosition)
    local useItem = config[item.itemid]
    if not useItem then
        return true
    end

    local player = Player(cid)
    local vocations = {1, 2, 5, 6}
    if item.itemid == 7440 then
        if not isInArray(vocations, player:getVocation():getBase():getId()) then
            doPlayerSendTextMessage(cid, 18 ,'Only sorcerers and druids may drink this fluid.', TALKTYPE_MONSTER_SAY)
            return true
        end
    end

    local cStorage = player:getStorageValue(Storage.Achievements.PotionAddict)
    if cStorage < 100000 then
        player:setStorageValue(Storage.Achievements.PotionAddict, math.max(1, cStorage) + 1)
    elseif cStorage == 100000 then
        player:addAchievement('Potion Addict')
        player:setStorageValue(Storage.Achievements.PotionAddict, 100001)
    end

    player:addCondition(useItem)
    player:getPosition():sendMagicEffect(CONST_ME_MAGIC_RED)
    Item(item.uid):remove(1)
    return true
end