I am trying to print a staff list with all the online staff members on the server

This is my code:

RegisterCommand('staff', function(source)
    local catistaff = 0
    local staff = vRP.getOnlineAdmins{};
    for k,v in pairs(staff) do
        local player = vRP.getUserSource{v}
        local name = GetPlayerName(player) or "Unknown"
        if name ~= "Unknown" then
            TriggerClientEvent('chatMessage', player, '^5' .. name .. ' ^0(^5' .. v .. '^0) -> ^1' .. vRP.getUserAdminTitle{v})
            catistaff = catistaff +1
        end
    end
    TriggerClientEvent('chatMessage', source, 'Staff Online: ^1' .. catistaff)
end)

And this is the error that I ve got:

[    c-scripting-core] InvokeNative: execution failed: Argument at index 1 was null.
[          script:vrp] SCRIPT ERROR: Execution of native 000000002f7a49e6 in script host failed: Argument at index 1 was null.
[          script:vrp] > [global chunk] (TriggerClientEventInternal.lua:3)
[          script:vrp] > sendStaffMessage (@vrp/modules/admin.lua:411)
[          script:vrp] > callback (@vrp/modules/admin.lua:317)
[          script:vrp] > handler (vrp-lib/Tunnel.lua:139)
[          script:vrp] null