title: SerialPort is Open but throws NullReferenceException on BytesToRead
body: <p>I have A SerialPort created, and can check it is not null, and that <a href="https://msdn.microsoft.com/en-us/library/system.io.ports.serialport.isopen(v=vs.110).aspx" rel="nofollow noreferrer">SerialPort.IsOpen()</a> returns true.
  But when I check the <a href="https://msdn.microsoft.com/en-us/library/system.io.ports.serialport.bytestoread(v=vs.110).aspx" rel="nofollow noreferrer">BytesToRead</a> Property I get a NullReferenceException.</p>
  
  <pre><code>NullReferenceException: Object reference not set to an instance of an object
    System.IO.Ports.WinSerialStream.get_BytesToRead ()
    System.IO.Ports.SerialPort.get_BytesToRead ()
    (wrapper remoting-invoke-with-check) 
    System.IO.Ports.SerialPort:get_BytesToRead ()
    ...
  </code></pre>
  
  <p>I can step through with the debugger and see that immedietly before the BytesToRead call, the Serial Port is Instantiated and Open, but the debugger can't reach certain properties, including BytesToRead.</p>
  
  <pre><code>"System.IO.Ports.SerialPort"
      base: "System.IO.Ports.SerialPort"
      BaseStream: {System.IO.Ports.WinSerialStream}
      BaudRate: 9600
      BreakState: false
      BytesToRead: System.NullReferenceException: Object reference not set to an instance of an object
      BytesToWrite: System.NullReferenceException: Object reference not set to an instance of an object
      CDHolding: false
      CtsHolding: true
      DataBits: 8
      DiscardNull: System.NotImplementedException: The requested feature is not implemented.
      DsrHolding: false
      DtrEnable: false
      Encoding: {System.Text.ASCIIEncoding}
      Handshake: None
      IsOpen: true
      NewLine: "\r\n"
      Parity: None
      ParityReplace: System.NotImplementedException: The requested feature is not implemented.
      PortName: "COM3"
      ReadBufferSize: 4096
      ReadTimeout: 50
      ReceivedBytesThreshold: System.NotImplementedException: The requested feature is not implemented.
      RtsEnable: false
      StopBits: One
      WriteBufferSize: 2048
      WriteTimeout: -1
  </code></pre>
  
  <p>What could be going wrong?</p>