Printer Error On Explotion

I have a printer that changes color rapidly with a 0.4 timer. When the printer explodes, an error comes up regarding a null entity. How do I fix this?

[ERROR] addons/tierprinters/lua/entities/tier5/cl_init.lua:17: Tried to use a NULL entity!

  1. SetColor - [C]:-1
  2. unknown - addons/tierprinters/lua/entities/tier5/cl_init.lua:17

http://pastie.org/10339734

when it explodes, stop the timer. this happened me a lot, easy to fix.

How do I do this?

[editline]9th August 2015[/editline]

include(“shared.lua”)

function ENT:Initialize()
end

local nextColorChange = 0

function ENT:Draw()

    self:DrawModel()
   
    if SysTime() >= nextColorChange then
           
            nextColorChange = SysTime() + 0.4 -- 0.4 means every 0.4 seconds it will change  colour
           
            local col = Color( math.random( 0, 255 ), math.random( 0, 255 ), math.random( 0, 255 ) )
            self:SetColor( col )
           
    end
   
    local Pos = self:GetPos()
    local Ang = self:GetAngles()
   
local owner = self:Getowning_ent()
    owner = (IsValid(owner) and owner:Nick()) or "unknown"
   
    txt1 = "Nuclear Printer"
    txt2 = "$" ..self:GetNWInt("PrintA")
   
    surface.SetFont("HUDNumber5")
    local TextWidth = surface.GetTextSize(txt1)
    local TextWidth2 = surface.GetTextSize(txt2)
    local TextWidth3 = surface.GetTextSize(owner)
   
    Ang:RotateAroundAxis(Ang:Up(), 90)
   
    cam.Start3D2D(Pos + Ang:Up() * 4.5, Ang, 0.11)
        draw.WordBox(2, -TextWidth3*0.5, -78, owner, "HUDNumber5", Color(0, 0, 0, 100), Color(255,255,255,255))
            draw.WordBox(2, -TextWidth*0.5, -30, txt1, "HUDNumber5", Color(0, 0, 0, 100), Color(255,255,255,255))
            draw.WordBox(2, -TextWidth2*0.5, 18, txt2, "HUDNumber5", Color(0, 0, 0, 100), Color(255,255,255,255))
    cam.End3D2D()

end

function ENT:Think()
end