if (callback.getCallbackName().equals("ob_gzhandler")) {
if (callback != null && callback.getCallbackName().equals("ob_gzhandler")) {
  public static boolean ob_start(Env env,                                 @Optional Callback callback,                                 @Optional int chunkSize,                                 @Optional("true") boolean erase)  {    if (callback.getCallbackName().equals("ob_gzhandler")) {      OutputBuffer ob = env.getOutputBuffer();      for (; ob != null; ob = ob.getNext()) {        Callback cb = ob.getCallback();        if (cb.getCallbackName().equals("ob_gzhandler")) {          env.warning(L.l("output handler 'ob_gzhandler' cannot be used twice"));          return false;        }      }    }        env.pushOutputBuffer(callback, chunkSize, erase);    return true;  }