23:54:35.755 Argument 1 missing or nil error? making projectile.

i need help with an error, when making my projectile it keeps saying, 23:54:35.755 Argument 1 missing or nil, and i've tried to fix the problem many times but it wouldnt work.

script.Parent.RemoteEvent.OnServerEvent:Connect(function(player, character)
	local char = player.Character or player.CharacterAdded:Wait()
	local root = character:WaitForChild("HumanoidRootPart")
	local fbtime = 4
	
	local MuseProjectile = game.ReplicatedStorage.Part:Clone()
	MuseProjectile.Parent = workspace
	MuseProjectile.CFrame = root.CFrame * CFrame.new (0,0,-2)
	game.Debris:AddItem(MuseProjectile, fbtime)
	
	local bodyvel = Instance.new("BodyVelocity")
	bodyvel.MaxForce = Vector3.new(1e8, 1e8,1e8)
	bodyvel.Velocity = root.CFrame.LookVector * 80
	bodyvel.Parent = MuseProjectile
	
	local debounce = false
	MuseProjectile.Touched:Connect(function(hit)
		if hit.isDescendantOf(char) then
			return
		end
		
		if hit.Parent:IsA("Accoutrement") then
			hit = hit.Parent
		end
		
		local enemyhumanoid = hit.Parent:WaitForChild("Humanoid")
		local enemyroot = hit.Parent:WaitForChild("HumanoidRootPart")
		if enemyhumanoid and not debounce then
			debounce = true
			MuseProjectile:Destroy()
			local HitM = game.ReplicatedStorage.Fire:Clone()
			HitM.Parent = enemyroot
			spawn(function()
				wait(.5)
				HitM.Enabled = false
				wait(.6)
				HitM.Destroy()
			end)
			enemyhumanoid:TakeDamage(25)
			wait()
			debounce = false
		end
	end)
end) 

In line 17, you should use colon when using functions like Instance:IsDescendantOf()

script.Parent.RemoteEvent.OnServerEvent:Connect(function(player, character)
	local char = player.Character or player.CharacterAdded:Wait()
	local root = character:WaitForChild("HumanoidRootPart")
	local fbtime = 4
	local MuseProjectile = game.ReplicatedStorage.Part:Clone()
	MuseProjectile.Parent = workspace
	MuseProjectile.CFrame = root.CFrame * CFrame.new (0,0,-2)
	game.Debris:AddItem(MuseProjectile, fbtime)
	
	local bodyvel = Instance.new("BodyVelocity")
	bodyvel.MaxForce = Vector3.new(1e8, 1e8,1e8)
	bodyvel.Velocity = root.CFrame.LookVector * 80
	bodyvel.Parent = MuseProjectile
	
	local debounce = false
	MuseProjectile.Touched:Connect(function(hit)
		if hit:IsDescendantOf(char) then -- line that had the error
			return
		end
		
		if hit.Parent:IsA("Accoutrement") then
			hit = hit.Parent
		end
	
		local enemyhumanoid = hit.Parent:WaitForChild("Humanoid")
		local enemyroot = hit.Parent:WaitForChild("HumanoidRootPart")
		if enemyhumanoid and not debounce then
			debounce = true
			MuseProjectile:Destroy()
			local HitM = game.ReplicatedStorage.Fire:Clone()
			HitM.Parent = enemyroot
			task.spawn(function()
				task.wait(.5)
				HitM.Enabled = false
				task.wait(.6)
				HitM.Destroy()
			end)
			enemyhumanoid:TakeDamage(25)
			task.wait()
			debounce = false
		end
	end)
end)

If you are using Instance.IsDescendantOf(), you have to specify the instance itself, like

--These two are the same
Instance.IsDescendantOf(Instance, char)
Instance:IsDescendantOf(char)

it automatically passes itself, useful for object-oriented programming