protected function getSlackWebhookUrl() {
    if ($this->getConfig()->has('slack.webhook-url')) {
      return $this->getConfigValue('slack.webhook-url');
    }
    elseif (getenv('SLACK_WEBHOOK_URL')) {
      return getenv('SLACK_WEBHOOK_URL');
    }

    $this->say("Slack webhook url not found. To enable Slack notifications, set <comment>slack.webhook-url</comment>.");
    return FALSE;
  }