simulator connection bug while select RS485

[masterchen]

In file ModbusServer.cs, line :388, when click accept button in setting page , clientConnectionThread is null, so it crashed.

` public void StopListening()
{
if (SerialFlag & (serialport != null))
{
if (serialport.IsOpen)
serialport.Close();
shouldStop = true;
}
try
{
tcpHandler.Disconnect();
listenerThread.Abort();

        }
        catch (Exception) { }
        listenerThread.Join();
        try
        {

            clientConnectionThread.Abort();
        }
        catch (Exception) { }
    }`

I found it was not initialised , after commiting out this line , it seems OK, can you help check ?@rossmann-engineering