"Argument 1 missing or nil" i dont know how to fix it, can someone help me?

So im trying to make a game similar to Pet Simulator X but with Missiles, and i tried making a chest opening system but the error pops out on line 51.

the error:

Argument 1 missing or nil - Client - ChestsClient:51 Stack Begin - Studio Script 'Players.UGA_BUGAGG.PlayerScripts.ChestsClient', Line 51 - function hatchChest -
Studio - ChestsClient:51 Stack End - Studio

the script:

local runService = game:GetService("RunService")
local replicatedStorage = game:GetService("ReplicatedStorage")
local players = game:GetService("Players")
local tweenService = game:GetService("TweenService")

local chests = workspace:WaitForChild("MainFolder_Workspace"):WaitForChild("Chests")
local remotes = replicatedStorage:WaitForChild("Remotes")
local pets = replicatedStorage:WaitForChild("Pets")

local player = players.LocalPlayer
local chestSystemSS = player:WaitForChild("PlayerGui"):WaitForChild("ChestSystem")
local chestViewport = chestSystemSS:WaitForChild("ChestViewport")

local function hatchChest(chestName, chosenPet)
    for _, v in pairs(player.PlayerGui:GetChildren()) do
        if v:IsA("ScreenGui") and v ~= chestSystemSS then
            v.Enabled = false
        end
    end
    chestSystemSS.Enabled = true
    for _, v in pairs(chestViewport:GetChildren()) do
        if v:IsA("Camera") or v:IsA("BasePart") or v:IsA("Model") then
            v:Destroy()
        end
    end
    chestViewport.Size = UDim2.fromScale(0, 0)
    local chestMesh = chests:FindFirstChild(chestName):Clone()
    chestMesh.Parent = chestViewport
    chestMesh.CFrame = CFrame.new(0, 0, 0)
    local camera = Instance.new("Camera")
    camera.Parent = chestViewport
    camera.CFrame = CFrame.new(0, 0, 4)
    chestViewport.CurrentCamera = camera
    tweenService:Create(chestViewport, TweenInfo.new(0.7), {Size = UDim2.new(0.604, 0,0.785, 0)}):Play()
    task.wait(0.7)
    for i = 1, 4 do
        tweenService:Create(chestViewport, TweenInfo.new(0.3, Enum.EasingStyle.Sine, Enum.EasingDirection.Out), {Rotation = 20}):Play()
        task.wait(0.3)
        tweenService:Create(chestViewport, TweenInfo.new(0.3, Enum.EasingStyle.Sine, Enum.EasingDirection.Out), {Rotation = -20}):Play()
        task.wait(0.3)
    end
    tweenService:Create(chestViewport, TweenInfo.new(0.3, Enum.EasingStyle.Sine, Enum.EasingDirection.Out), {Rotation = 0}):Play()
    task.wait(0.3)
    tweenService:Create(chestViewport, TweenInfo.new(0.7), {Size = UDim2.fromScale(0, 0)}):Play()
    task.wait (0.3)
    for _, v in pairs(chestViewport:GetChildren()) do
        if v:IsA("Camera") or v:IsA("BasePart") or v:IsA("Model") then
            v:Destroy()
        end
    end
    local petModel = pets:FindFirstChild(chosenPet.PetName):Clone()
    petModel:PivotTo(CFrame.new(0, 0, 0))
    petModel.Parent = chestViewport
    local cameraPet = Instance.new("Camera")
    cameraPet.Parent = chestViewport
    cameraPet.CFrame = CFrame.new(0, 0, -3.3) * CFrame.Angles(0, math.rad(180), 0)
    chestViewport.CurrentCamera = cameraPet
    tweenService:Create(chestViewport, TweenInfo.new(0.7), {Size = UDim2.new(0.27, 0,0.375, 0)}):Play()
    chestViewport.NameLabel.Text = chosenPet.PetName
    chestViewport.NameLabel.Visible = true
    chestViewport.RarityLabel.Text = chosenPet.Rarity
    chestViewport.RarityLabel.Visible = true
    task.wait (1.5)
    tweenService:Create(chestViewport, TweenInfo.new(0.3), {Size = UDim2.fromScale(0, 0)}):Play()
    task.wait (0.3)
    chestViewport.NameLabel.Visible = false
    chestViewport.RarityLabel.Visible = false
    for _, v in pairs(script.Parent:GetChildren()) do
        if v:IsA("ScreenGui") and v ~= chestSystemSS then
            v.Enabled = true
        end
    end
end

remotes:WaitForChild("HatchChest").OnClientEvent:Connect(hatchChest)