Review usage of null in returns

[jgoz]

Some methods that used to return null in v2.x now return non-null values (as discovered in #89). These should be reviewed and revised, if necessary.

[jasper22]

I develop small send/receive application in Windows and Linux based on ZeroMQ/clrzmq and found a small problem. I'm using REQ/REP sockets (Windows side is REP). There's a scenario when I don't care much about ZmqMessage that send back to Linux so I send it for example: socket.SendMessage( new ZmqMessage() ); Unfortunately Linux version of clrzmq crash with 'ENOENT' message code in Interop/SocketProxy/public byte[] Receive(byte[] buffer, int flags, out int size) function. Actually when you do P/Invoke to 'LibZmq.zmq_msg_recv' actual size in above condition come -1. I'm not sure if what I found related to your comment above but when I changed all messages to carry at least 1 byte buffer the whole system start to work

[jgoz]

@jasper22 Sorry for the delayed response.

The problem you experienced on Linux is not related to this issue. However, I did fix it a few days ago in 36cf1419aa. If you can, please pull the latest changes from master, rebuild the mono bindings, and test your application again.

Thank you for reporting this error.