X509 certificate creation issue

[Merlino]

I have this method to create the application certificate (it is taken directly from the example). If I add the commented code, the creation fails.
Can anybody tell me why?

  // Generate RSA Key
  QOpcUaKeyPair key;
  key.generateRsaKey(QOpcUaKeyPair::RsaKeyStrength::Bits2048);

  // Save private key to file
  const QByteArray keyData = key.privateKeyToByteArray(QOpcUaKeyPair::Cipher::Unencrypted, nullptr);
  Q_ASSERT(!keyData.isEmpty());

  QFile keyFile(privateKeyFilePath); // pem
  keyFile.open(QFile::WriteOnly);
  keyFile.write(keyData);
  keyFile.close();

  // Create a certificate signing request
  QOpcUaX509CertificateSigningRequest certificateSigningRequest;
  certificateSigningRequest.setEncoding(QOpcUaX509CertificateSigningRequest::Encoding::DER);

  // Set the subject of the certificate
  QOpcUaX509DistinguishedName distinguishedName;
  distinguishedName.setEntry(QOpcUaX509DistinguishedName::Type::CommonName, QCoreApplication::applicationName());
  distinguishedName.setEntry(QOpcUaX509DistinguishedName::Type::CountryName, CountryName);
  distinguishedName.setEntry(QOpcUaX509DistinguishedName::Type::LocalityName, LocalityName);
  distinguishedName.setEntry(QOpcUaX509DistinguishedName::Type::StateOrProvinceName, StateOrProvinceName);
  distinguishedName.setEntry(QOpcUaX509DistinguishedName::Type::OrganizationName, OrganizationName);
  certificateSigningRequest.setSubject(distinguishedName);

  // The subject alternative name extension is needed for OPC UA
  QOpcUaX509ExtensionSubjectAlternativeName* subjectAlternativeName = new QOpcUaX509ExtensionSubjectAlternativeName;
  //subjectAlternativeName->addEntry(QOpcUaX509ExtensionSubjectAlternativeName::Type::DNS, DNS);
  subjectAlternativeName->addEntry(QOpcUaX509ExtensionSubjectAlternativeName::Type::DNS, QHostInfo::localHostName());
  subjectAlternativeName->addEntry(QOpcUaX509ExtensionSubjectAlternativeName::Type::URI, getApplicationUri());
  subjectAlternativeName->setCritical(false);
  certificateSigningRequest.addExtension(subjectAlternativeName);

  // Set the certificate basic constraints
  QOpcUaX509ExtensionBasicConstraints* basicConstraints = new QOpcUaX509ExtensionBasicConstraints;
  basicConstraints->setCa(false);
  basicConstraints->setCritical(false);
  certificateSigningRequest.addExtension(basicConstraints);

  // Set the key usage constraints
  QOpcUaX509ExtensionKeyUsage* keyUsage = new QOpcUaX509ExtensionKeyUsage;
  keyUsage->setCritical(false);
  keyUsage->setKeyUsage(QOpcUaX509ExtensionKeyUsage::KeyUsage::DigitalSignature);
  keyUsage->setKeyUsage(QOpcUaX509ExtensionKeyUsage::KeyUsage::NonRepudiation);
  keyUsage->setKeyUsage(QOpcUaX509ExtensionKeyUsage::KeyUsage::KeyEncipherment);
  keyUsage->setKeyUsage(QOpcUaX509ExtensionKeyUsage::KeyUsage::DataEncipherment);
  keyUsage->setKeyUsage(QOpcUaX509ExtensionKeyUsage::KeyUsage::CertificateSigning);
  certificateSigningRequest.addExtension(keyUsage);

//  QOpcUaX509ExtensionExtendedKeyUsage* extendedKeyUsage = new QOpcUaX509ExtensionExtendedKeyUsage;
//  extendedKeyUsage->setCritical(false);
//  extendedKeyUsage->setKeyUsage(QOpcUaX509ExtensionExtendedKeyUsage::KeyUsage::TlsWebServerAuthentication);
//  extendedKeyUsage->setKeyUsage(QOpcUaX509ExtensionExtendedKeyUsage::KeyUsage::TlsWebClientAuthentication);
//  certificateSigningRequest.addExtension(extendedKeyUsage);

  const QByteArray selfSignedCertificateData = certificateSigningRequest.createSelfSignedCertificate(key, 12000/*days*/);
  Q_ASSERT(!selfSignedCertificateData.isEmpty());

  QFile certificateFile(certificateFilePath); // der
  certificateFile.open(QFile::WriteOnly);
  certificateFile.write(selfSignedCertificateData);
  certificateFile.close();