PlayerStatManager:ChangeStat return nill (repost)?

i have been following a book and have got to a point where it hasn't worked. when I touch the object it returns PlayerStatManager:changeStat returned nill. any help would be appreciated also sorry if you have seen this same Q before.

Module Script

local PlayerStatManager = {}

local DataStoreService = game:GetService("DataStoreService")

local playerData = DataStoreService:GetDataStore("PlayerData")

local AUTOSAVE_INTERVAL = 60
local DATASTORE_RETIES = 3
local sessionData = {}

function PlayerStatManager:ChangeStat(player,statName,changeValue)

	local playerUserId = "Player_"..player.UserId
	assert(typeof(sessionData[playerUserId][statName])== typeof(changeValue), "changestat error type doesnt match")
	if typeof(sessionData[playerUserId][statName]== "number") then
		sessionData[statName] = sessionData[playerUserId][statName]+changeValue
	else
			sessionData[playerUserId][statName] = changeValue
	end
	
end

local function dataStoreRetry(dataStoreFunction)
	local tries = 0
	local success = true
	local data = nil
	
	repeat 
	tries = tries + 1
	success = pcall(function() data = dataStoreFunction()end)
	
	if not success then
		wait(1)
		end
	until tries == DATASTORE_RETIES or success
	
	if not success then
		error("could not access DataStore")
	end
	return success, data
end

local function getPlayerData(player)
	return dataStoreRetry(function() 
	return playerData:GetAsync(player.UserId) 
	end)
end

local function savePlayerData(player)
	if sessionData[player] then
		return dataStoreRetry(function()
			return playerData:SetAsync(player.UserId,sessionData[player])
		end)
	end
end

local function setupPlayerData(player)
	local success, data = getPlayerData(player)
	if not success then
		sessionData[player] = false
	else
		if not data then
			sessionData[player] = {Aggressive = 0, AggressiveXp = 0, Timid = 0, TimidXp = 0, Large = 0, LargeXp = 0, Small = 0, SmallXp = 0, Hunting = 0}
			savePlayerData(player)
		else
				sessionData[player] = data
		end
	end
end

local function autosave()
	while wait(AUTOSAVE_INTERVAL) do
		for player, data in pairs(sessionData) do
			savePlayerData(player)
		end
	end
end

game.Players.PlayerAdded:Connect(setupPlayerData)
game.Players.PlayerRemoving:Connect(function(player)savePlayerData(player) sessionData[player] = nil
end)

spawn(autosave)
return PlayerStatManager

External scipt

local PlayerStatManager require(game.ServerScriptService.playerstatsmanager)

local huntingstart = script.Parent

local function IncreaseHunting(part)
	local hum = part.Parent:FindFirstChild("Humanoid")
	
	local plname = part.Parent.Name
	
	if hum then
		local player = game.Players:FindFirstChild(plname)
		
		PlayerStatManager:ChangeStat(player,"Hunting",5)
		huntingstart:Destroy()
	end
end

huntingstart.Touched:Connect(IncreaseHunting)