I need help fixing a Nil Value Problem, What does it mean? Can you help me understand this?

So, I have a problem, I'm trying to make a Ranking Script (To show the Player Rank above Name) and I (sometimes) get an Error:

Hectiq joined - Debug String
09:05:00.212 - ServerScriptService.Script:7: attempt to index upvalue 'team' (a nil value) - Error
09:05:00.212 - Stack Begin
09:05:00.213 - Script 'ServerScriptService.Script', Line 7
09:05:00.213 - Stack End
09:05:00.942 - ServerScriptService.RankingLabel:7: attempt to index upvalue 'team' (a nil value) - Error
09:05:00.943 - Stack Begin
09:05:00.943 - Script 'ServerScriptService.RankingLabel', Line 7
09:05:00.943 - Stack End

These are My Scripts (TeamList, RankingLabel)

RankingLabel:

local serverStorage = game:GetService("ServerStorage")
local bbg = serverStorage:WaitForChild("RankGui")
local team = _G.team

game.Players.PlayerAdded:Connect(function(player)
    game.Workspace:WaitForChild(player.Name)
    if team[player.Name] == "Owner" then
        local cbbg = bbg:Clone()
        cbbg.Parent = game.Workspace[player.Name].Head
        cbbg.Rank.Text = "Owner"
        cbbg.Rank.TextColor3 = Color3.fromRGB(170,0,0)
        return
    elseif team[player.Name] == "Designer" then
        local cbbg = bbg:Clone()
        cbbg.Parent = game.Workspace[player.Name].Head
        cbbg.Rank.Text = "Designer"
        cbbg.Rank.TextColor3 = Color3.fromRGB(0,0,223)
        return
    else
        local cbbg = bbg:Clone()
        cbbg.Parent = game.Workspace[player.Name].Head
        cbbg.Rank.Text = "Player"
        cbbg.Rank.TextColor3 = Color3.fromRGB(40,40,40)
        return
    end

end)

TeamList:

_G.team = {
    ["Hectiq"] = "Owner";
    ["CENSORED"] = "Designer";
}
return _G.team