调用函数时返回空值的表格

我正在尝试通过几个函数传递并返回一个表格，但只能到某个程度。我几乎确定它与作用域有关，但由于我是新手，所以无法解决。 我尝试将表格放在第1行并设置为全局，但无济于事。 错误：bag参数：预期得到表格，但得到了nil。

function returnToTunnel(movementTable)
    for i = table.maxn(movementTable), 1, -1  do  --这是我得到错误的地方。
        if (movementTable[i] == 1) then
            turtle.down()
        elseif (movementTable[i] == 2) then
            turtle.up()
        elseif (movementTable[i] == 3) then
            turtle.back()
            turtle.turnRight()
        elseif (movementTable[i] == 4) then
            turtle.back()
            turtle.turnLeft()
        elseif (movementTable[i] == 5) then
            turtle.back()
        end
    end
end

function mineOre(locationParam, movementTable)
    if (locationParam == 1) then
        turtle.digUp()
        turtle.suckUp()
        turtle.up()
        table.insert(movementTable, 1)
    elseif (locationParam == 2) then
        turtle.digDown()
        turtle.suckDown()
        turtle.down()
        table.insert(movementTable, 2)
    elseif (locationParam == 3) then
        turtle.turnLeft()
        turtle.dig()
        turtle.suck()
        turtle.forward()
        table.insert(movementTable, 3)
    elseif (locationParam == 4) then
        turtle.turnRight()
        turtle.dig()
        turtle.suck()
        turtle.forward()
        table.insert(movementTable, 4)
    elseif (locationParam == 5) then
        turtle.dig()
        turtle.suck()
        turtle.forward()
        table.insert(movementTable, 5)
    end
    locationParam = oreCheck()
    if (locationParam > 0) then
        mineOre(locationParam, movementTable)
    else
        return movementTable
    end
end

function digTunnel(tunnelLengthParam)
    local oreFound
    local movement = {}

    for i = 1, tunnelLengthParam do
        turtle.dig()
        turtle.forward()
        oreFound = oreCheck()
        if (oreFound > 0) then
            movement = mineOre(oreFound, movement)
            returnToTunnel(movement)
        end
        if ((i % 2) == 1) then
            turtle.digUp()
            turtle.up()
        elseif ((i % 2) == 0) then
            turtle.digDown()
            turtle.down()
        end
        oreFound = oreCheck()
        if (oreFound > 0) then
            movement = mineOre(oreFound, movement)
            returnToTunnel(movement)
        end
    end
end

因此，digTunnel函数调用了另外两个函数mineOre和returnToTunnel。

我已经查阅了LUA手册和几个网站，但无法解决问题。 感谢您的帮助！