All my backtests work, but when I go live, I get a runtime error:

Runtime Error: 'AAPL' wasn't found in the Slice object, likely because there was no-data at this moment in time and it wasn't possible to fillforward historical data. Please check the data exists before accessing it with data.ContainsKey("AAPL") in Slice.cs:line 315 Stack Trace: 'AAPL' wasn't found in the Slice object, likely because there was no-data at this moment in time and it wasn't possible to fillforward historical data. Please check the data exists before accessing it with data.ContainsKey("AAPL") in Slice.cs:line 315

How do I know if my code is good to trade live, because I don't get errors in my backtests?