When I trying change the value in my table with my modulescript I receive this error why?

ReplicatedFirst.PlayerStatManager:7: attempt to index field '?' (a nil value)

My ModuleScript:

local PlayerStatManager = {}

local sessionData = {}

function PlayerStatManager:ChangeStats(player, statName, changeValue, boolean)
	if boolean then
		sessionData[player][statName] = sessionData[player][statName] + changeValue
	else
		sessionData[player][statName] = sessionData[player][statName] - changeValue
	end
end

function PlayerStatManager:GetStats(player, statName)
	return sessionData[player][statName]
end

local function setupPlayerData(player)
	sessionData[player] = {Money= 0, Cursor = 0}
end

game.Players.PlayerAdded:connect(setupPlayerData)

return PlayerStatManager

My LocalScript:

-- My ModuleScript
local playerStatManager = require(game.ReplicatedFirst.PlayerStatManager)


-- My variables
local player = game.Players.LocalPlayer


local playerGui = player.PlayerGui
local moneyGui= playerGui:WaitForChild('MoneyGui')

local raward = moneyGui.Background.Stat.Money


-- My functions
function moneyGiver()
	playerStatManager:ChangeStats(player, 'Money', 1, true)
	raward.Text = '$ '..playerStatManager:GetStats(player, 'Money')	
end

giver.MouseButton1Click:connect(function()
	moneyGiver()
end)
Anonymous