Why is string value not allowed in data stores?

I've made multiple data stores before and this has never occurred. I'm making a new one rn and it gives me an error say "ServerScriptService.Saving:31: bad argument #3(string expected, got nil)". Is this even fixable?

game.Players.PlayerRemoving:Connect(function(player)
	local statstorage = game.ReplicatedStorage.PlayerData:FindFirstChild(player.UserId):GetChildren()
	for i =  1, #statstorage do
		local datastore = game:GetService("DataStoreService"):GetOrderedDataStore(statstorage[i].Name)
		datastore:SetAsync(player.UserId, statstorage[i].Value)
	end	
end)	

function Save(player)
	local statstorage  = game.ReplicatedStorage.PlayerData:FindFirstChild(player.UserId):GetChildren()
	for i =  1, #statstorage do
		local datastore = game:GetService("DataStoreService"):GetOrderedDataStore(statstorage[i].Name)
		datastore:SetAsync(player.UserId, statstorage[i].Value)
	end	
end

------------------------------------------------------------------------------

game.Players.PlayerAdded:Connect(function(player)
	spawn(function()
		while true do
			wait(600)
			Save(player)
		end
	end)
	game.ReplicatedStorage.PlayerData:WaitForChild(player.UserId)
	wait(1)
	local stats = game.ReplicatedStorage.PlayerData:WaitForChild(player.UserId):GetChildren()
	for i = 1, #stats do
	local datastore = game:GetService("DataStoreService"):GetOrderedDataStore(stats[i].Name)		
	stats[i].Value = datastore:GetAsync(player.UserId)
	end
end)