"attempt to index nil with 'FindFirstChild"' What's going on?

Hey, I'm currently working on a game, trying to make datastore's, but it doesnt work. This wont be about fixing datastores, because there is this one issue, where it basically cannot use FindFirstChild OR WaitForChild. Really annoying. Does anyone have a fix for this?

Leaderstats Module:

	local Leaderstats = {}
	
	-- Services
	local RunService = game:GetService("RunService")
	local DataStore = game:GetService("DataStoreService")
	local DataStoreKey = DataStore:GetDataStore("DataStore_6")
	local ReplicatedStorage = game:GetService("ReplicatedStorage")
	local Players = game:GetService("Players")
	
	local GameCore = require(ReplicatedStorage:WaitForChild("GameCore"))
	
	-- Misc
	local LeaderStats = script:WaitForChild("leaderstats")
	local Playerstats = script:WaitForChild("PlayerStats")
	
	-- Functions
	function Leaderstats.new(Player)
		
		local LsClone = LeaderStats:Clone()
		local PsClone = Playerstats:Clone()
		
		LsClone.Parent = Player
		PsClone.Parent = Player
		
	end
	
	function Leaderstats:LoadDataStore(Player)
		
		local Leaderstats = Player:FindFirstChild("leaderstats")
		local Money = Leaderstats:FindFirstChild("Money")
		
		local MoneyData
		local Success, Errormessage = pcall(function()
			
			warn("[!] Loading "..Player.Name.."'s data...")
			MoneyData = DataStoreKey:GetAsync(Player.UserId.." | money", Player.Leaderstats)
			
		end)
		
		if Success then
			warn("[!] Successfully loaded "..Player.Name.."'s data!")
		else
			warn("[!] Fatal Loading error: "..Errormessage)
		end
		
	end
	
	function Leaderstats:SaveDataStore(Player)
		
		local Leaderstats = Player:FindFirstChild("leaderstats")
		local Money = Leaderstats:FindFirstChild("Money")
		
		local success, errormessage = pcall(function()
			
			warn("[!] Saving "..Player.Name.."'s data...")
			DataStoreKey:SetAsync(Player.UserId.." | money", Player.Leaderstats)
			
		end)
		
		if success then
			warn("[!] Sucessfully saved "..Player.Name.."'s data!")
		else
			warn("[!] Fatal Saving error: "..errormessage)
		end
		
	end
	
	return Leaderstats

MainScript (script requiring the leaderstats module):

-- Services
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local ServerStorage = game:GetService("ServerStorage")
local TweenService = game:GetService("TweenService")
local Lightning = game:GetService("Lighting")
local RunService = game:GetService("TweenService")
local Players = game:GetService("Players")

-- Modules
local Bank = require(script.Bank)
local Leaderstats = require(script.Leaderstats)

local GameCore = require(ReplicatedStorage:WaitForChild("GameCore"))

-- Misc
local Sounds = ReplicatedStorage:WaitForChild("Sounds")

-- Functions


-- Code
Players.PlayerAdded:Connect(Leaderstats.new)
Players.PlayerAdded:Connect(Leaderstats.LoadDataStore)
Players.PlayerRemoving:Connect(Leaderstats.SaveDataStore)

Lightning.ClockTime = GameCore.StartTime

-- Spawn / While Loops

spawn(function() -- Day Light Loop
	
	print("Day Light Loop Started")
	
	while wait(1) do
		
		GameCore:Tween(1, "Sine", "Out", {ClockTime = Lightning.ClockTime + 1/45}, Lightning):Play()
		
			
		if math.floor(Lightning.ClockTime) == 6 then
				
			GameCore:Tween(1, "Sine", "Out", {Volume = 0.5}, Sounds:WaitForChild("DayAmbient")):Play()
			GameCore:Tween(1, "Sine", "Out", {Volume = 0}, Sounds:WaitForChild("NightAmbient")):Play()
			
		end
		
		if math.floor(Lightning.ClockTime) == 18 then
			
			GameCore:Tween(1, "Sine", "Out", {Volume = 0}, Sounds:WaitForChild("DayAmbient")):Play()
			GameCore:Tween(1, "Sine", "Out", {Volume = 0.5}, Sounds:WaitForChild("NightAmbient")):Play()
			
		end
			
	end
	
end)

spawn(function() -- Bank Loop
	
	print("Bank Loop Started")
	
	repeat wait() until math.floor(Lightning.ClockTime) == 11
	
	Bank:Open()
	
	print("Bank Opend")
	
	while wait(Bank.TimeToRob + 60) do
		
		Bank:Open()
		
		print("Bank Opend")
		
	end
	
end)

Help would seriously be helpful, I really don't know what to do. Thanks!