Problem wityh the plugin

Hello!
I have installed the plugin on my server.
Configuration:

{
	"Timeout": 60.0,
	"TradeCommand": "trade-command",
	"TradeListCommand": "trade",
	"AcceptTradeCommand": "atrade-command",
	"DeclineTradeCommand": "dtrade-command",
	"ShowUINotice": true,
	"UINoticeXOffset": 0.0,
	"UINoticeYOffset": 0.0,
	"TriggerCooldownOnDecline": true,
	"TeamOnlyTradingList": false,
	"Fee": {
		"Fee": 0,
		"DistanceThreshold": 500.0,
		"Currency Type (0 = None, 1 = Item, 2 = ServerRewards, 3 = Economics, 4 = Other": 0,
		"ItemShortName": "scrap",
		"ItemCustomName": "",
		"OtherSettings": {
			"PluginName": "MyCurrencyPlugin",
			"TypeMode (0 = Int, 1 = Double, 2 = Float)": 0,
			"FullName": "My Bank",
			"ShortName": "cc",
			"DepositMethod": "Deposit",
			"WithdrawMethod": "Withdraw",
			"BalanceMethod": "Balance"
		}
	},
	"Rules": {
		"CanTradeBuildingBlocked": false,
		"CanTradeCombatBlocked": false,
		"CanTradeRaidBlocked": false
	},
	"GroupCooldowns": null
}

After reloading plugin (oxide.reload StaticTrader) in the logs I see next message:
 

16:03 [Error] Failed to call hook 'OnServerInitialized' on plugin 'StaticTrader v1.2.4' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.StaticTrader.Loaded () [0x0006d] in <71a06ad90fb6408da8276fd79139af9c>:0
  at Oxide.Plugins.StaticTrader.OnServerInitialized () [0x00012] in <71a06ad90fb6408da8276fd79139af9c>:0
  at Oxide.Plugins.StaticTrader.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00142] in <71a06ad90fb6408da8276fd79139af9c>:0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <e23ba2c0f246426296d81c842cbda3af>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <50629aa0e75d4126b345d8d9d64da28d>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <50629aa0e75d4126b345d8d9d64da28d>:0
16:03 [Info] Loaded plugin StaticTrader v1.2.4 by Raul-Sorin Sorban

Please, could you clarify if I did something wrong or how can I fix it.
Thank you!

Thank you, it works!
But the only notice, that GroupCooldowns = null was generated by default (as default config).