Lua Code Problem

[EhsanReacher]

hi i have a error from this code

            --- < PERSONAGEM 2 > ---
            local sqll3 = dbPoll(dbQuery(Connection, "SELECT * FROM zn_users_saves WHERE serial = ?", ""..sserial.."-2p"), -1)
            for _33, roww3 in ipairs(sqll3) do
                if roww3 then
                    if getElementData(pv, "ZN-Logado") == false then
                        sid2 = roww3["id"]
                        snome2 = ""..roww3["nome"].." "..roww3["sobrenome"]..""
                        sidade2 = roww3["idade"]
                        snascimento2 = roww3["nascimento"]
                        sserial2 = roww3["serial"]
                    end
                    triggerClientEvent(pv, "ZN-CarregarPersonagensC2", root, sid2, snome2, sidade2, snascimento2, sserial2)
                end
            end

        end
    end
    setTimer(zncpersonagem, 50, 1)
end
-- zncpersonagem()
addEventHandler("onResourceStart", getResourceRootElement(getThisResource()), zncpersonagem)
 

error is attemp to concatenate global `serial ` <a nill value> 

this error is for this line

local sqll3 = dbPoll(dbQuery(Connection, "SELECT * FROM zn_users_saves WHERE serial = ?", ""..sserial.."-2p"), -1)

[CastiaL]

Did you assign a value to the "sserial" variable?