ServiceProxy creation before all replicas are ready

[Christoph-Denzel]

If a ServiceProxy is created before all replicas are ready and a reconnect is triggered in NettyClientServerCommunicationSystemClientSide and afterwards the replicas connect, but no message was issued, line 237 causes a NullPointerException.

[rvassantlal]

The client-side implementation was tested after the servers in the initial view were ready.
The code throws an exception because the mechanism for reconnecting assumes it will be used after the system is working correctly. If you start the client before the servers are ready, it schedules a reconnect and tries to send the previous message (which was null) after the connection with the servers is established.

Thank you for the report!