code: @Override
      public void onPreRemove(final IoFilterChain chain, final String name,
              final NextFilter nextFilter) {
          IoSession session = chain.getSession();
          session.removeAttribute(ProxyIoSession.PROXY_SESSION);
      }
docs: Called when the filter is removed from the filter chain.
  Cleans the {@link ProxyIoSession} instance from the session.
  
  @param chain the filter chain
  @param name the name assigned to this filter
  @param nextFilter the next filter