尝试索引字段“parent”（一个空值）

我尝试重新加载场景时遇到一些问题。

在我的程序中，用户可以用手指画一条线（这是一个 iOS/Android 应用程序），它运行得很好，但是，当我尝试重新加载场景时，控制台返回

“Attempt to index field 'parent' (a nil value)”

在第39行

我用于执行“drawline”和重新加载（在这种情况下是 replay）功能的代码是

local lines = {}
local lineGroup = display.newGroup()
local prevX,prevY
local isDrawing = true
local i = 1

local function distanceBetween(x1, y1, x2, y2)
local dist_x = x2 - x1
local dist_y = y2 - y1
local distanceBetween = math.sqrt((dist_x*dist_x) + (dist_y*dist_y))
return distanceBetween
end

local function drawLine(e)
if(e.phase == "began") then

    for i = #lines, 1, -1 do
  if (lines[i]) then
   lines[i].parent:remove(lines[i])
   lines[i] = nil
  end
end
lines = {}
line_number = 100

    prevX = e.x
    prevY = e.y
    isDrawing = true

elseif(e.phase == "moved") then
    local distance = distanceBetween(prevX, prevY, e.x, e.y)
    if(isDrawing and distance < 100) then
        if(lines[i]) then lineGroup:remove(i) end
        lines[i] = display.newLine(prevX, prevY, e.x, e.y)
        lines[i]:setColor(255, 255, 0)
        lines[i].width = 3
        lines[i].myName = "lines"

if(lines[i].y < 400) then
for i = #lines, 1, -1 do
  if (lines[i]) then
   lines[i].parent:remove(lines[i])
   lines[i] = nil
  end
end
end

        local dist_x = e.x - prevX
        local dist_y = e.y - prevY
        physics.addBody(lines[i], "static",
        { density = 1, friction = 0.5,
     bounce =  -0.8, shape = {0, 0, dist_x, dist_y,        0, 0} } )
        lineGroup:insert(lines[i])
    end

elseif(e.phase == "ended") then
    isDrawing = true
end

return lineGroup
end

Runtime:addEventListener("touch",drawLine)

其中第39行是 lines[i].parent:remove(lines[i])

有什么建议吗？谢谢！:)

** *_ THIS IS HOW I RESTART MY GAME *__**

--REPLAY

 local replayBTN = display.newImage("immagini/pause.png")

 replayBTN.alpha = 1
 replayBTN.x = _W/2
 replayBTN.y = _H/2

 localGroup:insert( replayBTN)

 function replay(event)
director:changeScene("game")
 return true
 end

 replayBTN:addEventListener("touch", replay)