What is the error in this script?

Hi, I'm having a problem with this code.

I'm testing on saving parts using Data Stores, but when I start a server and start a new player into the server, the output returns an error that I believe has been already fixed.

This picture is what the output returned.

This picture displays the hierarchy of the Explorer.

Note: There is just a bunch of parts inside the model that is inside the ServerStorage.

Do you know the solution to fix the error?

StructureStore = game:GetService("DataStoreService"):GetDataStore("StructureStore")
local structure = game:GetService("ServerStorage"):FindFirstChild("Structure_Player")

function PlayerEntered(player)
    local key = "Structure_"..player.Name
    repeat wait() until player.Character

    if StructureStore:GetAsync(key) ~= nil then
        StructureStore:GetAsync(key).Parent = game.Workspace
    else
        local structure_clone = structure:clone()
        structure_clone.Parent = game.Workspace
        structure_clone.Name = "Structure_"..player.Name
    end
end

function PlayerLeaving(plr)
    local key = "Structure_"..plr.Name
    StructureStore:SetAsync(key, game.Workspace["Structure_"..plr.Name])
end

game.Players.PlayerAdded:connect(PlayerEntered)
game.Players.PlayerRemoving:connect(PlayerLeaving)