code: public void close(final AVIMClientCallback callback) {
      final AVIMClientCallback internalCallback = new AVIMClientCallback() {
        @Override
        public void done(AVIMClient client, AVIMException e) {
          if (null == e) {
            AVIMClient.this.localClose();
          }
          if (null != callback) {
            callback.done(client, e);
          }
        }
      };
      InternalConfiguration.getOperationTube().closeClient(this.clientId, internalCallback);
    }
docs: close client.
  @param callback