Error message "attempt to index nil with UserId" in datastore, how can i fix it?

Im trying to make a datastore script but it wont save, it gives me the error message "attempt to index nil with UserId". I dont know how to fix it. Here is my code:

local datastoreservice = game:GetService("DataStoreService")
local datastorage = datastoreservice:GetDataStore("datastorage")
print("Variables loaded")

local function Load(player)
	local leaderstats = Instance.new("Folder")
	leaderstats.Name = "leaderstats"
	leaderstats.Parent = player
	
	local Nights = Instance.new("IntValue")
	Nights.Name = "Nights"
	Nights.Parent = leaderstats
	
	print("Leaderstats created")
	
	local data
	local success, errormessage = pcall(function()
		data = datastorage:GetAsync(player.UserId)
	end)
	print("Data load happened")
	
	if success then
		print("Data loaded")
	else
		warn("Error happened while loading data: "..errormessage)
	end
end

local function Save(player)
	local success, errormessage = pcall(function()
		datastorage:SetAsync(player.UserId, player.leaderstats.nights.Value)		
	end)	
	
	if success then
		print("Data saved")
	else
		warn("Error happened while saving data: "..errormessage)
	end
end

game.Players.PlayerAdded:Connect(Load)
game:BindToClose(Save)

Please help me, ive been having issues with datastoring for a few days

It could be because your local functions each have a parameter, which is player. But when you fire your functions, you're not giving them a parameter, so player is nil.

Here's your fixed script:

local DataStoreService = game:GetService("DataStoreService")
local DataStore = DataStoreService:GetDataStore("DataStore")
print("Variables Loaded")

function Load(player)
	local leaderstats = Instance.new("Folder",player)
	leaderstats.Name = "leaderstats"
	
	local nights = Instance.new("IntValue",leaderstats)
	nights.Name = "Nights"

	print("Leaderstats Loaded")

	local data

	local success,err = pcall(function()
		data = DataStore:GetAsync(player.UserId)
	end)
	
	if success then
		print("Data loaded!")
	else
		print("Error whilst loading player's data.")
	end
	nights.Value = data
end


function Save(player)
	local nights = player.leaderstats.Nights

	local success,err = pcall(function()
		DataStore:SetAsync(player.UserId, nights.Value)
	end)
	
	if success then
		print("Data saved!")
	else
		print("Error whilst saving player's data.")
	end
end

game.Players.PlayerAdded:Connect(function(plr)
	Load(plr)
end)

game.Players.PlayerRemoving:Connect(function(plr)
	Save(plr)
end