Add this validation in line 291 inside the IF before the count: 

args != null && ​

The whole function is:

[ChatCommand("info")]
        private void ShowInfo(BasePlayer player, string command, string[] args)
        {
            if (player == null || _settings == null)
                return;

            if (!PlayerActiveTabs.ContainsKey(player.userID))
                PlayerActiveTabs.Add(player.userID, new PlayerInfoState(_settings));

            var container = new CuiElementContainer();
            var mainPanelName = AddMainPanel(container);
            PlayerActiveTabs[player.userID].MainPanelName = mainPanelName;

            var tabFirstIndex = _settings.TabToOpenByDefault;
            var tabToSelectIndex = tabFirstIndex;
            int tabtoSelectArgumentIndex = 0;
            if (args != null && args.Count() == 1)
            {
                if (int.TryParse(args[0], out tabtoSelectArgumentIndex))
                {
                    tabToSelectIndex = tabtoSelectArgumentIndex;
                    PlayerActiveTabs[player.userID].ActiveTabIndex = tabtoSelectArgumentIndex;
                }
            }

            var allowedTabs = _settings.Tabs
                .Where((tab, tabIndex) => string.IsNullOrEmpty(tab.OxideGroup) ||
                    tab.OxideGroup.Split(',')
                        .Any(group => Permission.UserHasGroup(player.userID.ToString(CultureInfo.InvariantCulture), group)))
                .ToList();
            if (allowedTabs.Count <= 0)
            {
                SendReply(player, "[GUI Help] You don't have permissions to see info.");
                return;
            }

            var activeAllowedTab = allowedTabs[tabToSelectIndex];
            var tabContentPanelName = CreateTabContent(activeAllowedTab, container, mainPanelName);
            var activeTabButtonName = AddActiveButton(tabToSelectIndex, activeAllowedTab, container, mainPanelName);


            for (int tabIndex = 0; tabIndex < allowedTabs.Count; tabIndex++)
            {
                if (tabIndex == tabToSelectIndex)
                    continue;

                AddNonActiveButton(tabIndex, container, allowedTabs[tabIndex], mainPanelName, activeTabButtonName);
            }
            PlayerActiveTabs[player.userID].ActiveTabContentPanelName = tabContentPanelName;
            SendUI(player, container);
        }