DefaultSmppClient#destroy NPE in netty4 branch

[krasa]

Run com.cloudhopper.smpp.demo.ClientMain without a server:

2015-04-13 17:04:21,110 [nioEventLoopGroup-2-1] TRACE c.c.s.c.SmppClientConnector - channelRegistered
2015-04-13 17:04:21,110 [main] DEBUG c.c.smpp.impl.DefaultSmppClient - Waiting for client connection to /127.0.0.1:2776
2015-04-13 17:04:22,116 [nioEventLoopGroup-2-1] TRACE c.c.s.c.SmppClientConnector - channelUnregistered
2015-04-13 17:04:22,119 [main] WARN  c.c.smpp.impl.DefaultSmppClient - Client did not connect.
java.net.ConnectException: Connection refused: no further information: /127.0.0.1:2776
    at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method) ~[na:1.7.0_72]
    at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:739) ~[na:1.7.0_72]
    at io.netty.channel.socket.nio.NioSocketChannel.doFinishConnect(NioSocketChannel.java:208) ~[netty-all-4.0.25.Final.jar:4.0.25.Final]
    at io.netty.channel.nio.AbstractNioChannel$AbstractNioUnsafe.finishConnect(AbstractNioChannel.java:281) ~[netty-all-4.0.25.Final.jar:4.0.25.Final]
    at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:528) ~[netty-all-4.0.25.Final.jar:4.0.25.Final]
    at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:468) ~[netty-all-4.0.25.Final.jar:4.0.25.Final]
    at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:382) ~[netty-all-4.0.25.Final.jar:4.0.25.Final]
    at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:354) ~[netty-all-4.0.25.Final.jar:4.0.25.Final]
    at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:116) ~[netty-all-4.0.25.Final.jar:4.0.25.Final]
    at io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:137) ~[netty-all-4.0.25.Final.jar:4.0.25.Final]
    at java.lang.Thread.run(Thread.java:745) ~[na:1.7.0_72]
2015-04-13 17:04:22,120 [main] ERROR c.c.smpp.demo.ClientMain - 
com.cloudhopper.smpp.type.SmppChannelConnectException: Unable to connect to host [127.0.0.1] and port [2776]: Connection refused: no further information: /127.0.0.1:2776
    at com.cloudhopper.smpp.impl.DefaultSmppClient.createConnectedChannel(DefaultSmppClient.java:321) ~[classes/:na]
    at com.cloudhopper.smpp.impl.DefaultSmppClient.doOpen(DefaultSmppClient.java:232) ~[classes/:na]
    at com.cloudhopper.smpp.impl.DefaultSmppClient.bind(DefaultSmppClient.java:201) ~[classes/:na]
    at com.cloudhopper.smpp.demo.ClientMain.main(ClientMain.java:110) ~[test-classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.7.0_72]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) ~[na:1.7.0_72]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.7.0_72]
    at java.lang.reflect.Method.invoke(Method.java:606) ~[na:1.7.0_72]
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140) [idea_rt.jar:na]
Caused by: java.net.ConnectException: Connection refused: no further information: /127.0.0.1:2776
    at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method) ~[na:1.7.0_72]
    at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:739) ~[na:1.7.0_72]
    at io.netty.channel.socket.nio.NioSocketChannel.doFinishConnect(NioSocketChannel.java:208) ~[netty-all-4.0.25.Final.jar:4.0.25.Final]
    at io.netty.channel.nio.AbstractNioChannel$AbstractNioUnsafe.finishConnect(AbstractNioChannel.java:281) ~[netty-all-4.0.25.Final.jar:4.0.25.Final]
    at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:528) ~[netty-all-4.0.25.Final.jar:4.0.25.Final]
    at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:468) ~[netty-all-4.0.25.Final.jar:4.0.25.Final]
    at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:382) ~[netty-all-4.0.25.Final.jar:4.0.25.Final]
    at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:354) ~[netty-all-4.0.25.Final.jar:4.0.25.Final]
    at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:116) ~[netty-all-4.0.25.Final.jar:4.0.25.Final]
    at io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:137) ~[netty-all-4.0.25.Final.jar:4.0.25.Final]
    at java.lang.Thread.run(Thread.java:745) ~[na:1.7.0_72]
2015-04-13 17:04:22,121 [main] INFO  c.c.smpp.demo.ClientMain - Shutting down client bootstrap and executors...
Exception in thread "main" java.lang.NullPointerException
    at com.cloudhopper.smpp.impl.DefaultSmppClient.destroy(DefaultSmppClient.java:153)
    at com.cloudhopper.smpp.demo.ClientMain.main(ClientMain.java:183)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140)

[jjlauer]

That's a nice find. Do you think you would have time to submit a fix and PR?