NullReferenceException happens randomly when item is hovered

[ihor-rud]

Happens quite consistently after ~5 min of using. Makes search completely broken.

Failed to fetch market data.
	System.AggregateException: One or more errors occurred. (Object reference not set to an instance of an object.)
	 ---> System.NullReferenceException: Object reference not set to an instance of an object.
	   at MarketBoardPlugin.GUI.MarketBoardWindow.<RefreshMarketData>b__54_2(MarketDataResponse data)
	   at System.Linq.Enumerable.TryGetFirst[TSource](IEnumerable`1 source, Func`2 predicate, Boolean& found)
	   at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source, Func`2 predicate, TSource defaultValue)
	   at MarketBoardPlugin.GUI.MarketBoardWindow.<RefreshMarketData>b__54_0()
	   --- End of inner exception stack trace ---
Inner exception
	System.NullReferenceException: Object reference not set to an instance of an object.
	   at MarketBoardPlugin.GUI.MarketBoardWindow.<RefreshMarketData>b__54_2(MarketDataResponse data)
	   at System.Linq.Enumerable.TryGetFirst[TSource](IEnumerable`1 source, Func`2 predicate, Boolean& found)
	   at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source, Func`2 predicate, TSource defaultValue)
	   at MarketBoardPlugin.GUI.MarketBoardWindow.<RefreshMarketData>b__54_0()