Datastore is returning nil...?

local Data = game:GetService("DataStoreService"):GetDataStore("Saves")
local HS = game:GetService("HttpService")

local Shirts = game.Workspace.Sir.Shirts

game.Players.PlayerAdded:connect(function(player)

    local PKey = "user_" .. player.userId


    local Stats = Instance.new("Model",player)
    Stats.Name = "UserStat"
    local SavesLists = HS:JSONDecode((Data:GetAsync(PKey)))


    local ShirtColor = Instance.new("StringValue",Stats)
    ShirtColor.Name = "ShirtColor"
    ShirtColor.Value = tostring(SavesLists[1])


    local ShirtType = Instance.new("StringValue",Stats)
    ShirtType.Name = "ShirtType"
    ShirtType.Value = tostring(SavesLists[2])


    if tostring(ShirtColor.Value) == "" then ShirtColor.Value = "Institutional white" end
    if tostring(ShirtType.Value) == "" then ShirtType.Value = "1" end


    for i,v in pairs(Shirts:GetChildren()) do
    for i,d in pairs(v:GetChildren()) do
    if d:IsA("BasePart") then
    if d.Parent.Name ~= "Shirt"..ShirtType then
    d.Transparency = 1
    else
    d.Transparency = 0
    end
    d.BrickColor = BrickColor.new(ShirtColor.Value)
    end
    end
    end


    function Update()
    local Table = {ShirtColor.Value,ShirtType.Value}
    local SavesList = HS:JSONEncode(Table)
    Saves:SetAsync(P, SavesList)
    end


    ShirtColor.Changed:connect(function(Val)
    Update()
    end)

    ShirtType.Changed:connect(function(Val)
    Update()
    end)


end)

Output:

Argument 1 missing or nil at line 13