Tried to make random map system.but an error invalid argument #2 to 'random' (interval is empty)?

Server script (in serverscriptservice):

local lobby_Duration = 10
local round_Duration = 10
local maps = game:GetService('ReplicatedStorage'):WaitForChild('Map'):GetChildren()
local timerval = game.ReplicatedStorage:WaitForChild("TimerValue")

local function RTimer ()
    while wait() do
        for l = lobby_Duration, 0, -1 do
            timerval.Value = 'Intermission: '..l
            wait(1)

            if l == 0 then
                local map = maps[math.random(1, #maps)] -- this is the problem
                timerval.Value = 'Teleporting players to '..map.Name 
                wait(1)
                map.Parent = workspace

                local players = game.Players:GetChildren()

                for i = 1, #players do
                    players[i].Character:MoveTo(Vector3.new(-122.5, 55.5, -41.5))
                end

                wait(1)

                for g = round_Duration,0, -1 do
                    timerval.Value = 'Round '..g..' seconds left'
                    wait(1)

                    if g == 0 then
                        timerval.Value = 'Round over'
                        wait(2)
                        timerval.Value = 'Teleporting players to lobby'
                        wait(1)
                        for i = 1, #players do
                            players[i].Character:MoveTo(Vector3.new(-122.5, 55.5, 32.5))
                        end

                        map.Parent = maps
                        wait(1)
                        -- repeat again
                    end
                end
            end
        end
    end
end

spawn(RTimer)