java求助

本人是一java菜鸟，有如下代码，

    @Override
public void disconnect(IConnection conn, IScope scope) {
String uid = conn.getClient().getId();
String username = clientMgr.removeClient(scope, uid);
IConnections.remove(conn);
UserIDs.remove(username);
        for(int ii=0;ii<LeaveIDs.size();ii++){
            if(username.indexOf(LeaveIDs.get(ii))>=0){
                 LeaveIDs.remove(ii);
            }
        }
for(int ii=0;ii<IConnections.size();ii++){
IServiceCapableConnection service = (IServiceCapableConnection) IConnections.get(ii);
service.invoke("ServerCall_UserList_LoginOutUser", new Object[] { username });
}
if(username.indexOf("`")>0){ExecUrl(StrUrl,"");}
super.disconnect(conn, scope);
}

出错如下错误：

INFO   | jvm 1    | 2012/11/15 10:33:38 | [ERROR] 2012-11-15 10:33:38,312 pool-3-thread-16:( org.red5.server.Scope.disconnect ) Error while executing "disconnect" for connection RTMPMinaConnection from 111.78.97.75:15713 to 122.0.67.37:21 (in: 3954, out: 4544) on handler org.red5.first.Application@199197b
INFO   | jvm 1    | 2012/11/15 10:33:38 | java.lang.NullPointerException
INFO   | jvm 1    | 2012/11/15 10:33:38 | at org.red5.first.Application.disconnect(Unknown Source)
INFO   | jvm 1    | 2012/11/15 10:33:38 | at org.red5.server.Scope.disconnect(Scope.java:493)
INFO   | jvm 1    | 2012/11/15 10:33:38 | at org.red5.server.BaseConnection.close(BaseConnection.java:304)
INFO   | jvm 1    | 2012/11/15 10:33:38 | at org.red5.server.net.rtmp.RTMPConnection.close(RTMPConnection.java:565)
INFO   | jvm 1    | 2012/11/15 10:33:38 | at org.red5.server.net.rtmp.RTMPMinaConnection.close(RTMPMinaConnection.java:57)
INFO   | jvm 1    | 2012/11/15 10:33:38 | at org.red5.server.net.rtmp.BaseRTMPHandler.connectionClosed(BaseRTMPHandler.java:237)
INFO   | jvm 1    | 2012/11/15 10:33:38 | at org.red5.server.net.rtmp.RTMPMinaIoHandler.sessionClosed(RTMPMinaIoHandler.java:232)
INFO   | jvm 1    | 2012/11/15 10:33:38 | at org.apache.mina.common.support.AbstractIoFilterChain$TailFilter.sessionClosed(AbstractIoFilterChain.java:550)
INFO   | jvm 1    | 2012/11/15 10:33:38 | at org.apache.mina.common.support.AbstractIoFilterChain.callNextSessionClosed(AbstractIoFilterChain.java:269)
INFO   | jvm 1    | 2012/11/15 10:33:38 | at org.apache.mina.common.support.AbstractIoFilterChain.access$800(AbstractIoFilterChain.java:53)
INFO   | jvm 1    | 2012/11/15 10:33:38 | at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.sessionClosed(AbstractIoFilterChain.java:633)
INFO   | jvm 1    | 2012/11/15 10:33:38 | at org.apache.mina.filter.executor.ExecutorFilter.processEvent(ExecutorFilter.java:230)
INFO   | jvm 1    | 2012/11/15 10:33:38 | at org.apache.mina.filter.executor.ExecutorFilter$ProcessEventsRunnable.run(ExecutorFilter.java:264)
INFO   | jvm 1    | 2012/11/15 10:33:38 | at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
INFO   | jvm 1    | 2012/11/15 10:33:38 | at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
INFO   | jvm 1    | 2012/11/15 10:33:38 | at java.lang.Thread.run(Unknown Source)

看这句：at org.red5.first.Application.disconnect(Unknown Source)
关键是Unknown Source，我要怎么修改，
希望贴代码 --------------------编程问答-------------------- (Scope.java:493)
看看这个。  你报了空指针自己看看那个对象是不是为null --------------------编程问答-------------------- (Scope.java:493)这个文件是已编译好的，不是我写的，我写的是上面的代码 --------------------编程问答-------------------- 关键是这个错误，不是一调试就出得来的，是很多天后，偶尔报这个错 --------------------编程问答-------------------- 这段代码，要怎么修改，才能彻底避免这个错误

补充：Java ,  Java相关