How do I fix a userdata value bug?

I got some code from the "Map Chooser" wiki page from roblox. On a part of the script, it chooses a map. It picks from a folder called maps which is located in the ReplicatedStorage.

This is the line of code it is in (inside a function called "pickMap"):

local selectedIndex = math.random(1, #maps)
local map = mapList[selectedIndex]:Clone()

"maps" is a variable outside the function:

local maps = replicatedStorage:WaitForChild("Maps")

This is the error I get: ServerScriptService.Script:9: attempt to get length of upvalue 'maps' (a userdata value)

If you want the whole page of code, search "Map Chooser" on the roblox wiki.

maps is a ROBLOX Object, probably a Model. You need to use GetChildren on it to get a Table:

local maps = replicatedStorage:WaitForChild("Maps"):GetChildren()