How to fix "Invalid argument #2 (string expected, got nil) error?

The error happens on the teamPlayer function: "local newTeam = playerFrame[team]" On line 94

local playersService = game:GetService('Players');
local localPlayer = playersService.LocalPlayer;
local localName = localPlayer.Name;

local leaderboardGUI = script.Parent;
local mainFrame = leaderboardGUI.mainFrame;
local playersFrame = mainFrame.playersFrame;
local listLayout = playersFrame.UIListLayout;
local nameLabel = mainFrame.nameLabel;
local rankStatusLabel = mainFrame.rankStatusLabel;
local prisonTimeStatusLabel = mainFrame.prisonTimeStatusLabel;
local playerFrame = script.playerFrame:Clone();
script.playerFrame:Destroy();
local teamFrame = script.teamFrame:Clone();
script.teamFrame:Destroy();

local players = {};

local replicatedStorage = game:GetService('ReplicatedStorage');
local networkEvent = replicatedStorage.networkEvent;
local networkFunction = replicatedStorage.networkFunction;

local newUDim2 = UDim2.new;
local tabKeyCode = Enum.KeyCode.Tab;
local coroutineWrap = coroutine.wrap;

game:GetService('StarterGui'):SetCoreGuiEnabled(Enum.CoreGuiType.PlayerList, false);

local function resizePlayersFrame()
    local totalY = 0;
    for i, v in next, playersFrame:GetChildren() do
        if v:IsA('ImageLabel') and v.Visible then
            totalY = totalY + v.Size.Y.Offset + 3;
        end;
    end;
    playersFrame.CanvasSize = newUDim2(0, 0, 0, totalY);
end;

listLayout:GetPropertyChangedSignal('AbsoluteContentSize'):Connect(function()
    resizePlayersFrame();
end);

for i, v in next, game:GetService('Teams'):GetChildren() do
    local teamName = v.Name;
    local teamFrame = teamFrame:Clone();
    teamFrame.Name = teamName;
    teamFrame.nameLabel.Text = teamName;
    teamFrame.ImageColor3 = v.TeamColor.Color;
    teamFrame.Visible = false;
    teamFrame.LayoutOrder = i - 1;
    teamFrame:GetPropertyChangedSignal('Visible'):Connect(function()
        resizePlayersFrame();
    end);
    teamFrame.Parent = playersFrame;
end;

local function addPlayer(name, premium, rank, prisonTime)
    local playerFrame = playerFrame:Clone();
    playerFrame.nameLabel.Text = name;
    playerFrame.premiumImage.Visible = premium;
    playerFrame.rankStatusLabel.Text = rank;
    --playerFrame.prisonTimeStatusLabel.Text = prisonTime;
    playerFrame.Parent = playersFrame;
    return playerFrame;
end;

local function updatePlayer(name, status, data)
    if not players[name] then return; end;
    players[name][1][status .. 'Label'].Text = data;
end;

local function removePlayer(name)
    if not players[name] then return; end;
    local oldTeam = players[name][2];
    players[name][1]:Destroy();
    players[name] = nil;
    if oldTeam then
        local found = false;
        for i, v in next, players do
            if v[2] == oldTeam then
                found = true;
                break;
            end;
        end;
        if not found then
            playersFrame[oldTeam].Visible = true;
        end;
    end;
end;

local function teamPlayer(name, team)
    if not players[name] then return; end;
    local oldTeam = players[name][2];
    local newTeam = playersFrame[team];
    if not newTeam.Visible then
        newTeam.Visible = true;
    end;
    players[name][1].LayoutOrder = newTeam.LayoutOrder;
    players[name][2] = team;
    if oldTeam then
        local found = false;
        for i, v in next, players do
            if v[2] == oldTeam then
                found = true;
                break;
            end;
        end;
        if not found then
            playersFrame[oldTeam].Visible = false;
        end;
    end;
end;

for i, v in next, playersService:GetPlayers() do
    coroutineWrap(function()
        local name, premium, rank, prisonTime, team = networkFunction:InvokeServer('GetPlayerData', v);
        if name then
            if not players[name] then
                players[name] = {addPlayer(name, premium, rank, prisonTime, team)};
                teamPlayer(name, team);
            end;
        end;
    end)();
end;

networkEvent.OnClientEvent:Connect(function(event, ...)
    if event == 'NewPlayer' then
        local name, premium, rank, prisonTime, team = ...;
        if players[name] then return; end;
        players[name] = {addPlayer(...)};
        teamPlayer(name, team);
    elseif event == 'UpdatePlayer' then
        if ({...})[1] == localName then 
            local name, status, data = ...;
            if status == 'prisonTimeStatus' then
                prisonTimeStatusLabel.Text = data;
            elseif status == 'rankStatus' then
                rankStatusLabel.Text = data;
            end;
        end;
        updatePlayer(...);
    elseif event == 'TeamPlayer' then
        teamPlayer(...);
    elseif event == 'RemovePlayer' then
        removePlayer(...);
    end;
end);

if not localPlayer:IsDescendantOf(game) then
    localPlayer:GetPropertyChangedSignal('Parent'):Wait();
end;

nameLabel.Text = localPlayer.Name;
rankStatusLabel.Text = localPlayer:GetRoleInGroup(3151317);
prisonTimeStatusLabel.Text = localPlayer:WaitForChild('leaderstats'):WaitForChild('Prison Time').Value;

game:GetService('UserInputService').InputBegan:Connect(function(input, onGUI)
    if onGUI then return; end;
    if input.KeyCode == tabKeyCode then
        leaderboardGUI.Enabled = not leaderboardGUI.Enabled;
    end;
end);