docs: private X509TrustManager defaultTrustManager() throws GeneralSecurityException {
      TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance(
          TrustManagerFactory.getDefaultAlgorithm());
      trustManagerFactory.init((KeyStore) null);
      TrustManager[] trustManagers = trustManagerFactory.getTrustManagers();
      if (trustManagers.length != 1 || !(trustManagers[0] instanceof X509TrustManager)) {
        throw new IllegalStateException("Unexpected default trust managers:"
            + Arrays.toString(trustManagers));
      }
      return (X509TrustManager) trustManagers[0];
    }