Argument 1 missing or nil

What the message means

ServerScriptService.Spawner:6: Argument 1 missing or nil

Other forms of the same message:

• Argument 2 missing or nil
• Argument 3 missing or nil

Built-in Luau functions word the same mistake as invalid argument #1 to 'x' (table expected, got nil). Roblox's own functions say Argument N missing or nil.

For a method called with a colon, such as folder:FindFirstChild(name), argument 1 is name: the object before the colon is not counted.

Causes and fixes

Three things cause this error in practice. Each one below has the smallest code that triggers it, then the fix.

• The value you passed was never set
• The argument was left out
• A RemoteEvent value arrived as nil

The value you passed was never set

A variable, attribute or table entry that was never set is nil. Passing it on to a Roblox method that needs a value, such as the name in FindFirstChild, fails on that call rather than where the value went missing.

local button = workspace:WaitForChild("TeleportButton")
local targets = workspace:WaitForChild("Targets")

-- the button has no "Target" attribute, so this is nil:
-- Argument 1 missing or nil
local target = targets:FindFirstChild(button:GetAttribute("Target"))
print(target)

Read the value into a variable, check it, and only then pass it on. Set the attribute in the Properties window (Attributes, then +).

local button = workspace:WaitForChild("TeleportButton")
local targets = workspace:WaitForChild("Targets")

local targetName = button:GetAttribute("Target")
if typeof(targetName) ~= "string" then
	warn("[Teleporter] TeleportButton has no Target attribute")
	return
end
local target = targets:FindFirstChild(targetName)
print(target)

The argument was left out

Some calls need a value that is easy to forget, such as the name in FindFirstChild() or the class in IsA().

local folder = workspace:WaitForChild("Enemies")

-- no name given: Argument 1 missing or nil
local boss = folder:FindFirstChild()
print(boss)

Pass every value the function needs. Each method's page in the Creator Docs lists its parameters; the ones without a default are required.

local folder = workspace:WaitForChild("Enemies")

local boss = folder:FindFirstChild("Boss")
print(boss)

A RemoteEvent value arrived as nil

A client can fire a RemoteEvent with fewer values than the server expects (or with an Instance the server cannot see, which arrives as nil). The handler then passes nil into an engine call.

local ReplicatedStorage = game:GetService("ReplicatedStorage")

local equip = ReplicatedStorage:WaitForChild("Equip")

-- the client called equip:FireServer() with no tool name:
equip.OnServerEvent:Connect(function(player, toolName)
	-- toolName is nil: Argument 1 missing or nil
	local tool = player.Backpack:FindFirstChild(toolName)
	print(tool)
end)

On the server, check every value a client sends: its type, and that it is an object the server knows. Send names or IDs and look the object up on the server instead of trusting the client.

local ReplicatedStorage = game:GetService("ReplicatedStorage")

local equip = ReplicatedStorage:WaitForChild("Equip") :: RemoteEvent

equip.OnServerEvent:Connect(function(player: Player, toolName: unknown)
	if typeof(toolName) ~= "string" then
		return
	end
	local backpack = player:FindFirstChildOfClass("Backpack")
	local tool = backpack and backpack:FindFirstChild(toolName)
	if tool and tool:IsA("Tool") then
		print(player.Name, "has", tool.Name)
	end
end)

How to find the line that causes it

1. Open Output (Window menu, or the Script tab), clear it with Ctrl+K (⌘K on Mac), and press Play.
2. Find the first red line. It starts with the script's place in the Explorer and the line number, such as ServerScriptService.Shop:12:.
3. Click the red line. Studio opens that script with the cursor on the failing line.
4. Read the lines between Stack Begin and Stack End under it: they list the calls that led there, newest first, so you can see which function called the broken one.
5. Still not sure which value is wrong? Add print(typeof(x), x) just above the line, or set a breakpoint on it and read the values in the Watch window.

Questions

Sources and further reading

• Roblox Creator Docs: Instance:GetAttribute. returns nil when the attribute is not set
• Roblox Creator Docs: remote events and callbacks. what can be sent, and Instances the receiver cannot see arriving as nil
• Roblox Creator Docs: Instance:FindFirstChild

How the code was checked: every block marked Fixed passes Luau's strict type checker against Roblox's API definitions (luau-lsp, 23 October 2026), and every block marked Breaks compiles and fails only when it runs. The message wording was checked against the message strings in Roblox Studio itself (macOS build of 13 October 2026) on 23 October 2026. A type check catches misspelt APIs and wrong types, not game logic, so playtest in Studio before you publish.