!1 修复im-server空指针bug

Merge pull request !1 from blue/v_1.0.0

im-server/src/main/java/com/bx/imserver/websocket/WebsocketChannelCtxHolder.java

@@ -18,16 +18,16 @@ public class WebsocketChannelCtxHolder {
     }
 
     public static void  removeChannelCtx(Long userId){
+        if(userId != null){
             channelMap.remove(userId);
         }
+    }
 
     public static ChannelHandlerContext  getChannelCtx(Long userId){
-        return channelMap.get(userId);
+        if(userId == null){
+            return  null;
         }
-
+        return channelMap.get(userId);
-    public static Set<Long> getAllChannelIds(){
-        return channelMap.keySet();
     }
 
-
 }