bad argument #1 to 'random' (number expected, got nil)

出现问题，可能是使用了 math.random?

这是代码：

local combat = createCombatObject()
setCombatParam(combat, COMBAT_PARAM_EFFECT, CONST_ME_MAGIC_BLUE)
setCombatParam(combat, COMBAT_PARAM_AGGRESSIVE, false)

function onGetFormulaValues(cid, level, maglevel)
    local min = (((level/5)+(maglevel*1) +1))
    local max = (((level/5)+(maglevel*2) +3))
    return min, max
end

setCombatCallback(combat, CALLBACK_PARAM_LEVELMAGICVALUE, "onGetFormulaValues")

local condition = createConditionObject(CONDITION_REGENERATION)
setConditionParam(condition, CONDITION_PARAM_SUBID, 1)
setConditionParam(condition, CONDITION_PARAM_BUFF, true)
setConditionParam(condition, CONDITION_PARAM_TICKS, 1 * 60 * 1000)
setConditionParam(condition, CONDITION_PARAM_HEALTHGAIN, math.max(math.random(min, max)))
setConditionParam(condition, CONDITION_PARAM_HEALTHTICKS, 1000)
setCombatCondition(combat, condition)

function onCastSpell(cid, var)
    return doCombat(cid, combat, var)
end

它说错误在第17行，即 math.random。我对Lua的了解很少，这段代码是我从一个论坛中得到的，那个人在2012年发帖，所以我无法询问他们。