Fix possible NPE. See #274

example/src/main/java/io/netty/example/proxy/HexDumpProxyInboundHandler.java

@@ -100,10 +100,12 @@ public class HexDumpProxyInboundHandler extends SimpleChannelUpstreamHandler {
         // the incoming traffic from the outboundChannel.
         synchronized (trafficLock) {
             if (e.getChannel().isWritable()) {
+                if (outboundChannel != null) {
                     outboundChannel.setReadable(true);
                 }
             }
         }
+    }
 
     @Override
     public void channelClosed(ChannelHandlerContext ctx, ChannelStateEvent e)