Attempt to perform arithmetic on nil value?

[CafeMarsh]

Hey what's going on Facepunch?

I'm trying to make Keypads and Keypad Crackers obsolete by replacing them with an axe that breaks doors down. Anywho, in doing this, I had to assign each door entity hitpoints so the SWEP would know if the door is ready to be opened or not. This can be viewed below.

--#NoSimplerr#

local Door = FindMetaTable("Entity")

function Door:SetDoorHp(hp)
if IsValid(self) then
if self:isDoor() then
self.hp = hp
end
end
end

function Door:GetDoorHp()
if not IsValid(self) then return end
if self:GetClass() == "func_door" then return end
if self:isDoor() then
return self.hp
end
end

hook.Add("InitPostEntity", "RefreshDoorHp", function()
-- Set the hp on all doors
for k, v in pairs(ents.GetAll()) do
v:SetDoorHp(100)
end

end)

That's how I assigned health to the door. I did this in /addons/darkrpmodification/darkrp_modules/doorhp/sh_door.lua

Then, in /addons/darkrpmodification/weapons/weapon_breaker, I actually have the SWEP that takes some HP off the doors.

AddCSLuaFile()

-- Information about the SWEP
if CLIENT then
SWEP.PrintName = "Door Breaker"
SWEP.Author = "CafeMarsh"
SWEP.Instructions = "Rapidly left-click to deduct material health of door / prop."
SWEP.Slot = 5
SWEP.SlotPos = 120
end

-- Spawning
SWEP.Category = "DarkRP (Weapon)"
SWEP.Spawnable = true
SWEP.AdminOnly = true

-- Primary
SWEP.Primary.ClipSize = -1
SWEP.Primary.DefaultClip = -1
SWEP.Primary.Automatic = false
SWEP.Primary.Ammo = "none"

-- Secondary
SWEP.Secondary.ClipSize = -1
SWEP.Secondary.DefaultClip = -1
SWEP.Secondary.Automatic = false
SWEP.Secondary.Ammo = "none"

-- Player info about the SWEP
SWEP.Weight = 5
SWEP.AutoSwitchTo = false
SWEP.AutoSwitchFrom = false

-- Ammunition
SWEP.DrawAmmo = false
SWEP.DrawCrosshair = true

-- Models
SWEP.ViewModel = "models/weapons/v_diamond_mc_pickaxe.mdl"
SWEP.WorldModel = "models/weapons/w_diamond_mc_pickaxe.mdl"

local HitSound = Sound("pl_burnpain1.wav")
local oooBaby = Sound("triple.mp3")

-- Hit the door and take door HP away
function SWEP:PrimaryAttack()
if not IsFirstTimePredicted() then return end
self.Weapon:SetNextPrimaryFire(CurTime() + 0.5)

local tr = self.Owner:GetEyeTrace()
if tr.Entity:GetClass() == "func_door" then return end

if not IsValid(tr.Entity) then return end
if tr.Entity:GetClass() == "prop_door_rotating" then
if tr.Entity:GetPos():Distance(self.Owner:GetPos()) < 100 then
self:EmitSound(HitSound)

tr.Entity:SetDoorHp(tr.Entity:GetDoorHp() - 10)

if tr.Entity.Fire and tr.Entity:GetDoorHp() <= 0 then
tr.Entity:keysUnLock()
tr.Entity:Fire("open", "", .6)
tr.Entity:Fire("setanimation", "open", .6)
tr.Entity:SetDoorHp(100)
end

self.Owner:PrintMessage(HUD_PRINTTALK, tr.Entity:GetDoorHp())
end
end

end

function SWEP:SecondaryAttack()
self.Weapon:SetNextSecondaryFire(CurTime() + 120)
self:EmitSound(oooBaby)
end

Anyway, I noticed a few strange things about this.
First of all, the line that says
self.Owner:PrintMessage(HUD_PRINTTALK, tr.Entity:GetDoorHp())
runs twice (e.g: I hit the door once, and the updated HP is printed twice, regardless of IsFirstTimePredicted() being ran)

Secondly, I get script errors that state
[ERROR] addons/darkrpmodification/lua/weapons/weapon_breaker/shared.lua:58: attempt to perform arithmetic on a nil value
  1. unknown - addons/darkrpmodification/lua/weapons/weapon_breaker/shared.lua:58
when I left-click on any door OUTSIDE of spawn, and with this script error,
self.Owner:PrintMessage(HUD_PRINTTALK, tr.Entity:GetDoorHp())
is only ran once...

PLEASE HELP

[SweptThrone]

It seems like you're running everything on both realms, client and server. Player:PrintMessage is a shared function, which means it will be called once on the server, and once on the client. IsFirstTimePredicted() doesn't change this (if I'm right...)
This could also be the problem with the nil value, since it might only be set on the server.
It's hard to tell anything definitely, but I think that might be what's going on.

[CafeMarsh]

Yeah, I just based the fix on what you said and I speculated the same thing and it definitely fixed it. Appreciate you!