How do you remove a viewmodel after it's unequipped?

I am trying to remove the viewmodel after my tool is unequipped but this happens.

"Model:SetPrimaryPartCFrame() failed because no PrimaryPart has been set, or the PrimaryPart no longer exists. Please set Model.PrimaryPart before using this."

After it's destroyed it say's the error. I tried to use clone but it doesn't fix it.

local cam = workspace.CurrentCamera

local player = game.Players.LocalPlayer

local viewmodel = game.ReplicatedStorage.viewmodel:Clone()

viewmodel.Parent = cam

local character = player.Character

viewmodel.PrimaryPart = viewmodel.HumanoidRootPart

local runservice = game:GetService("RunService")

local gunTool = nil

local function setcam()

while guntool and runservice.RenderStepped:Wait() do

	viewmodel:SetPrimaryPartCFrame(cam.CFrame*CFrame.new(0.5, -0.5, -1))
end

end

character.ChildAdded:Connect(function(child)

if child:IsA("Tool") and child.Name == "FastCastGun" then

	guntool = child
	setcam()
          if viewmodel.Parent == game:GetService("ReplicatedStorage") then
		viewmodel:Clone() -- I tried to use this to fix but still it says the error
		viewmodel.Parent = cam
	end
end

end)

character.ChildRemoved:Connect(function(child)

if child and child == guntool then
	
	guntool = nil --maybe here's the problem
        viewmodel:Destroy() -- or this 
end

end)

Looking at this function:

local function setcam()
	while guntool and runservice.RenderStepped:Wait() do
		viewmodel:SetPrimaryPartCFrame(cam.CFrame*CFrame.new(0.5, -0.5, -1))
	end
end

The while loop is still running even after the viewmodel is destroyed. A simple fix would be to add the viewmodel variable into the while loop's condition. I believe this should work:

local function setcam()
	while guntool and viewmodel and runservice.RenderStepped:Wait() do
		viewmodel:SetPrimaryPartCFrame(cam.CFrame*CFrame.new(0.5, -0.5, -1))
	end
end