So I'm trying to make a rank system that's based on the player's level, but when I tried to make it it did not work. Is it even possible to do this, and if it's not is there any other way?

---//Error\---

ServerScriptService.LeaderStats.RankHandler:9: invalid argument #3 (string expected, got nil)

--//RankScript\---

---//Services\\---
local ReplicatedStorage = game:GetService("ReplicatedStorage")
--//ServiceChildren\\--
local USRankHandler = require(ReplicatedStorage.RankHandler:WaitForChild("USRankHandler"))
local VRankHandler = require(ReplicatedStorage.RankHandler:WaitForChild("VRankHandler"))
---//Script\\---
game.Players.PlayerAdded:Connect(function(player)
	if player.TeamColor == BrickColor.new("Cyan") then
		player:WaitForChild("leaderstats").Rank.Value = USRankHandler.Rank(player:WaitForChild("leaderstats2").Level.Value) ---Rank is a StringValue level is a IntValue

		player.leaderstats2.Level:GetPropertyChangedSignal("Value"):Connect(function()
			player:WaitForChild("leaderstats").Rank.Value = USRankHandler.Rank(player:WaitForChild("leaderstats2").Level.Value)
		end)
	end
end)

---//ModuleScript\---

local USRank = {}

local players = game.Players
local player = players.LocalPlayer

USRank.Rank = function(USR)
	
	if USR == 1 then
		USR = "Private"
			
	elseif USR == 2 then
		USR = "PFC"
			
	elseif USR == 3 then
		USR = "Corporal"
			
	elseif USR == 4 then
		USR = "Sergeant"

	elseif USR == 5 then
		USR = "Staff Sergeant"

	elseif USR == 6 then
		USR = "Technical Sergeant"

	elseif USR == 7 then
		USR = "First Sergeant"

	elseif USR == 8 then
		USR = "Master Sergeant"

	elseif USR == 9 then
		USR = "Second Lieutenant"

	elseif USR == 10 then
		USR = "First Lieutenant"

	elseif USR == 11 then
		USR = "Captain"

	elseif USR == 12 then
		USR = "Major"

	elseif USR == 13 then
		USR = "Lieutenant Colonel"

	elseif USR == 14 then
		USR = "Colonel"

	elseif USR == 15 then
		USR = "Brigadier General"

	elseif USR == 16 then
		USR = "Major General"

	elseif USR == 17 then
		USR = "Lt.General"

	elseif USR == 18 then
		USR = "General"

	elseif USR == 19 then
		USR = "General of the army"

	elseif USR >= 20 then
		USR = (USR).."CINC"
	end
end

return USRank

---//P.S\---

I'm new to module scripts. So please understand why I'm having a hard time with something like this.