TFS 1.2 - Summon Spell Bug

[Kouki]

Hello, i try to do "Summon Emberwing Spell"
I find code here: Lua - Summon floorchange (https://otland.net/threads/summon-floorchange.250838/)
but when i use this spell on normal char i got client crash, on god char i can use it.
Someone know why i got this?

local combat = createCombatObject()
setCombatParam(combat, COMBAT_PARAM_TYPE, COMBAT_NONE)
setCombatParam(combat, COMBAT_PARAM_EFFECT, CONST_ME_MORTAREA)
setCombatFormula(combat, COMBAT_FORMULA_LEVELMAGIC, 0, 0, 0, 0)
local maxsumons = 1
function onCastSpell(creature, variant)
    local summoncount = #creature:getSummons()
    if summoncount < 1 then
        for i = 1, maxsumons - summoncount do
            local summon = Game.createMonster("Emberwing", creature:getPosition())
            if summon ~= nil then
                summon:setMaster(creature)
            end
        end
    end
    return combat:execute(creature, variant)
end