Why is setAsync giving me error?

Alright, so I have a module script which contains a bunch of methods for storing, changing, and getting player data. There is a table called sessionData which stores players. Attached to each player is a set of identical data(values may be different, but there is the same number of keys and all key names are the same). The problem arises when I try call setAsync in the module script.

sessionData var

local sessionData = {}

This data table is copied to each player if getAsync returns nil(meaning this player doesn't have an existing data set

data = {Coins = 0, Gold = 0, Level = 1, cpCurrent = 0, 
			cpMax = 0, cpPerLvl = 0, cpRecovery = 0, expCurrent = 0, 
			expNeeded = 0, hpMax = 75, hpPerLvl = 0.15}

After creating a data set for new players, it sets the data to an index in sessionData which can be referenced by the player

sessionData[player] = data

Tries to call this method but returns an error, both after setting a new data set and for saving data which are the two times in the module script that setAsync() is called

playerData:SetAsync(player.UserId, sessionData[player])

Note: These methods are called in another script using PlayerAdded and PlayerRemoving and the player object passed from both these events is passed on to the function via parameter.

This is the error

13:00:10.748 - Argument 2 missing or nil
13:00:10.751 - Script 'ServerStorage.PlayerStatManager', Line 27 - method savePlayerData
13:00:10.753 - Script 'Workspace.setup', Line 8
13:00:10.755 - Stack End

PlayerAdded and PlayerRemoving regular script located in workspace

local module = require(game.ServerStorage.PlayerStatManager)

game.Players.PlayerAdded:connect(function(player)
	module:setupPlayerData(player) --SetAsync() in this method returns error
end)

game.Players.PlayerRemoving:connect(function(player)
	module:savePlayerData(player) --SetAsync() in this method returns an error
end)

I have completely redone this question. If you have any problems or errors, contact me ASAP. I hope you thumbs up this post as I have put a lot of work on it.

I am using JSON as a string / table saver. In my head JSON is a much better way of data saving. http://wiki.roblox.com/index.php?title=JSON http://wiki.roblox.com/index.php?title=API:Class/HttpService/JSONEncode http://wiki.roblox.com/index.php?title=API:Class/HttpService/JSONDecode http://wiki.roblox.com/index.php?title=API:Class/HttpService

Your server script..

local mod = require(game.ServerStorage.PlayerStatManager)
local players = game:GetService("Players")

players.PlayerAdded:connect(function(Player)
	local _DS_Result = mod:getPlayerData(Player, "Datastore")
	if _DS_Result ~= nil then
		mod:UpdateSessionData(Player, "Data", _DS_Result)
	else
		local Result = mod:setupPlayerData(Player)
		if type(Result) ~= "table" then
			error("Result ~= table")
		end
	end
end)

players.PlayerRemoving:connect(function(Player)
	mod:savePlayerData(Player)
end)

And now, for the longggggg module for any type of data :)

local sessionData			={}
local playerData			=game:GetService("DataStoreService"):GetDataStore("playerData")
local Http					=game:GetService("HttpService")
local JSONEncode			=function(...) return(Http:JSONEncode(...)) end
local JSONDecode			=function(...) return(Http:JSONDecode(...)) end
local GetInfo				=function(plr, data) for _,v in next,sessionData do if v.User:lower() == plr.Name:lower() then return(v[data]) end end return(nil) end
local SetInfo				=function(plr, data_name, set_data) for _,v in next,sessionData do if v.User:lower() == plr.Name:lower() then if GetInfo(plr, data_name) then v[data_name] = set_data return v[data_name] else return"Unable to get data" end end end return(nil) end

local NewUserData			={
	Coins = 0, 
	Gold = 0, 
	Level = 1, 
	cpCurrent = 0, 
    cpMax = 0, 
	cpPerLvl = 0, 
	cpRecovery = 0, 
	expCurrent = 0, 
    expNeeded = 0, 
	hpMax = 75, 
	hpPerLvl = 0.15
}

function sessionData:UpdateSessionData(Player, Data_Name, Data) -- Update the sessionData table, mid-game if you need
	local Result = SetInfo(Player, Data_Name, Data)
	if Result == nil then
		warn("Somethings not right here!")
	else
		print("Updated sessionData for "..Player.Name)
	end
end

function sessionData:setupPlayerData(Player) -- For a player that has just joined, never before
	table.insert(sessionData, {User=Player.Name; Data=nil;}) -- Insert new data
	SetInfo(Player, "Data", NewUserData)
	local JSON			=JSONEncode( GetInfo(Player, "Data") ) -- Convert a table to a string
	playerData:SetAsync(Player.UserId, JSON) -- Set the table as a string
	return JSONDecode( playerData:GetAsync(Player.UserId) ) -- When we return it to check, its now a table!
end

function sessionData:savePlayerData(Player) -- For a player thats leaving the server
	local JSON 			=JSONEncode( GetInfo(Player, "Data") ) -- Convert to a string, gets the sessionData's table
	playerData:SetAsync(Player, JSON)
	return JSONDecode( playerData:GetAsync(Player.UserId) )
end

function sessionData:getPlayerData(Player, String)
	if String == "Datastore" then
		return JSONDecode( playerData:GetAsync(Player.UserId) ) -- Returns a table
	elseif String:lower() == "SessionData" then
		return GetInfo(Player, "Data") -- Also returns a table ;)
	else
		warn("To call getPlayerData you need for #arg2 either, \"Datastore\" or \"SessionData\"!")
		return(nil)
	end
end

return sessionData