DataStore SetAsync isn't saving?

I have been making a saving system that loads all the items you have equipped or that are in the backpack from your last session. When it loads it says that the datastore is nil

Error: https://gyazo.com/9a41cf4de4c9c4f6c6a18bc5ff20cea5

Few disclaimers so that you are able to digest the code.

Function returnBackpack returns the items that is in the players backpack and items that are currently being equipped as a table. Disclaimer: This functions 100% works

local dss = game:GetService('DataStoreService')
local datastore = dss:GetDataStore('StoreData')

function generateDataKey(player)
    local ret = "uid_" .. player.UserId
    return ret
end
function returnBackpack(plr,val)
    if val ~= 'removing' then
        local tbl = {}
        for i,v in pairs(plr.Backpack:GetChildren()) do
            table.insert(tbl,v.Name)
        end
        for i,v in pairs(plr.Character:GetChildren()) do
            if v:IsA('Tool') then
                table.insert(tbl,v.Name)
            end
        end
        return tbl
    else
        local tbl = {}
        for i,v in pairs(plr.Backpack:GetChildren()) do
            table.insert(tbl,v.Name)
        end
        local charTool = game.ReplicatedStorage.changed:InvokeClient(plr)
        if charTool ~= nil then
            table.insert(tbl,charTool)
        end
        return tbl
    end
end
function saveDataForPlayer(player,val)
    if val ~= 'removing' then
        local key = generateDataKey(player)
        local data = returnBackpack(player)
        local success, err = pcall(function()
            datastore:SetAsync(key, data)
        end)
    else
        local key = generateDataKey(player)
        local data = returnBackpack(player,'removing')
        local success, err = pcall(function()
            datastore:SetAsync(key, data)
        end)
    end
end
function loadDataForPlayer(player)
    local char = player.Character or player.CharacterAdded:Wait()
    local key = generateDataKey(player)
    local data = datastore:GetAsync(key)
    for i,v in pairs(data) do
        local x = game.ServerStorage.Store[v]:Clone()
        x.Parent = game.Players[player.Name].Backpack
    end
end
game.Players.PlayerAdded:Connect(function(player)
    loadDataForPlayer(player)
end)
game.Players.PlayerRemoving:Connect(function(player)
    saveDataForPlayer(player,'removing')
end)

Note: This error is not because it is my first time joining the server. I have made sure to test that possibility.

Any help would be appreciated

EDIT: I found the error; when player removing was called, all items in the backpack were removed, and the local script was destroyed, so I had to manually update a table every time a player equipped or unequipped an item to overcome this issue.