public function getOptions()
  {
    $options = [
      'trace'      => $this->getTrace(),
      'cache_wsdl' => $this->getCache(),
      'classmap'   => $this->getClassmap(),
    ];

    if ($this->certificate) {
      $options['local_cert'] = $this->certificate;
    }

    $this->options = array_merge($options, $this->options);

    return $this->options;
  }