Entity Not Found

I have code to close a trade if the price goes below its stoploss as a backup.  I have seen situations where the broker did not trigger the SL because it jumped over the value.

But the main issue here is that it will return a "entity not found" error if the server closes the trade first. How can I check for the existence of the position before modifying the trade or closing it?

Here is the code I use in the OnTick event to check

            foreach (var position in Positions)
            {
                if (position!=null && position.TradeType==TradeType.Buy && position.StopLoss!=null && Symbol.Bid<position.StopLoss)
                {
                    Log(paramIntLogEnable, paramExtLogEnable,"Sending Manuel SL Close of {0}", position.Label);
                    if (ClosePosition(position).IsSuccessful && Positions.Count == 0) return;
                }
                
                if (position!=null && position.TradeType==TradeType.Sell && position.StopLoss!=null && Symbol.Ask>position.StopLoss)
                {
                    Log(paramIntLogEnable, paramExtLogEnable,"Sending Manuel SL Close of {0}", position.Label);
                    if (ClosePosition(position).IsSuccessful && Positions.Count == 0) return;
                }
            }