Value is not changing after the humanoid dies, anyone know why?

Regular script in workspace.

local human = script.Parent.Humanoid
human.Died:Connect(function(player)
		player.leaderstats.Experience.Value = player.leaderstats.Experience.Value + 5
end)

Basically, if the player kills the enemy, the value "experience" should increase by 5, but it doesn't, instead it gives me this " 16:53:46.035 - Workspace.Model.Zombie.EXPGiver:3: attempt to index local 'player' (a nil value)". Anyone could tell me what causes this error message and how to make this script work?

The error is saying that the player is never defined.

The died function doesn't return any result, thus you are getting a nil result.

You need some script that adds the player's name to the enemy, something like (I'll do in pseudo code):

If player hurts enemy, overwrite "whoHitEnemy" (a string variable, maybe in the enemy's humanoid) to player name

so then (in code):

local human = script.Parent.Humanoid
human.Died:Connect(function()
	local whoHitName = Humanoid.whoHitEnemey.Value
	local player
	if game.Players:FindFirstChild(whoHitName) then
		player = game.Players:FindFirstChild(whoHitName)
	end
	if player==nil then
	else
       	player.leaderstats.Experience.Value = player.leaderstats.Experience.Value + 5
	end
end)

Roblox tools insert an object value into the humanoid named "creator" this script should help

script.Parent.Humanoid.creator.Value.leaderstats.Experience.Value = script.Parent.Humanoid.creator.Value.leaderstats.Experience.Value + 5