Why do I get this error? Please read before reviewing code.

The error shows up at line 11 (The clicked function) It works in studio but not ingame. I tried waiting for the mouse but it just waits infinitely. The error that shows up (without the waiting) is "attempt to index local 'mouse' (a nil value)". I've checked and everything seems to be fine. when I changed mouse = player:GetMouse() to mouse = player (thinking maybe player was already the mouse), it said: Hit is not a part of Player.

part = script.Parent.PrimaryPart
mouseClicked = false
partMoving = false
collision = false
isincollision = false
originalcolor = {}
outOfBounds = false

function clicked(player)
    mouse = player:GetMouse()
    playerSlot = PlayerSlot(player)
    for i,v in pairs(script.Parent:GetChildren()) do
        local increment = 0
        if v.ClassName == "Part" then
            increment = increment+1
            table.insert(originalcolor, v.BrickColor)
        end
    end
    if mouseClicked == false then
        mouseClicked = true
        if partMoving == false then
            partMoving = true
            wait()
            mouseClicked = false
            MovePart(player)
        else
            wait()
            mouseClicked = false
            PlacePart(player)
        end
    end
end

function RoundUp(number)
    local roundNumber = number-(number%0.5)
    return roundNumber
end

function MovePart(player)
    local mouse = player:GetMouse()
    while partMoving == true do
        script.Parent:SetPrimaryPartCFrame(CFrame.new((RoundUp(mouse.Hit.p.x)), script.Parent.PrimaryPart.CFrame.Y, (RoundUp(mouse.Hit.p.Z))))
        wait()
    end
end

function PlacePart(player)
    local mouse = player:GetMouse()
    if isincollision == false then
        if outOfBounds == false then
            partMoving = false
        end
    end
end

script.Parent.PrimaryPart.Changed:connect(function()
    for i,modelpart in pairs(script.Parent:GetChildren()) do
        if modelpart.ClassName == "Part" then
            for i,part in pairs(modelpart:GetTouchingParts()) do
                if part.Parent ~= script.Parent then
                    if collision == false then
                        collision = true
                    end
                end
            end
        end
    end
    if collision ~= false then
        isincollision = true
        for i,v in pairs(script.Parent:GetChildren()) do
            if v.ClassName == "Part" then
                if v.BrickColor ~= BrickColor.new("Really red") then
                    v.BrickColor = BrickColor.new("Really red")
                    v.Transparency = 0.5
                end
            end
        end
    else
        isincollision = false
        local increment = 0
        if outOfBounds == false then
            for i,v in pairs(script.Parent:GetChildren()) do
                if v.ClassName == "Part" then
                    increment = increment+1
                    local color = tostring(originalcolor[increment])
                    if v.BrickColor == BrickColor.new("Really red") then
                        v.BrickColor = BrickColor.new(color)
                        v.Transparency = 0
                    end
                end
            end
        end
    end
    collision = false
end)

function PlayerSlot(player)
    for i,v in pairs(game.Workspace.Slots:GetChildren()) do
        if v.Slot_Owner.Value == player.Name then
            print(v)
            return v
        end
    end
end

script.Parent.PrimaryPart.Changed:connect(function()
    local partSize = script.Parent.PrimaryPart.Size
    local partPos = script.Parent.PrimaryPart.CFrame
    local slotPosX = playerSlot.slot.Position.X
    local slotPosZ = playerSlot.slot.Position.Z
    local slotSizeX = playerSlot.slot.Size.X
    local slotSizeZ = playerSlot.slot.Size.Z
    local oneOutOfBounds = false

    if oneOutOfBounds == false then
        if partPos.X + partSize.X/2 > slotPosX+slotSizeX/2 then
            oneOutOfBounds = true
        elseif partPos.X - partSize.X/2 < slotPosX-slotSizeX/2 then
            oneOutOfBounds = true
        end
    end

    if oneOutOfBounds == false then
        if partPos.Z + partSize.Z/2 > slotPosZ+slotSizeZ/2 then
            oneOutOfBounds = true
        elseif partPos.Z - partSize.Z/2 < slotPosZ-slotSizeZ/2 then
            oneOutOfBounds = true
        end
    end

    if oneOutOfBounds == true then
        outOfBounds = true
        for i,v in pairs(script.Parent:GetChildren()) do
            if v.ClassName == "Part" then
                if v.BrickColor ~= BrickColor.new("Really red") then
                    v.BrickColor = BrickColor.new("Really red")
                    v.Transparency = 0.5
                end
            end
        end
    else
        outOfBounds = false
    end
end)

script.Parent.ClickDetector.MouseClick:connect(clicked)