code: @Override
      public Set<String> getSupportedExtensions() {
          if (supportedExts == null) {
              supportedExts = new HashSet<String>(4);
              supportedExts.add(CertificatePolicies_Id.toString());
              supportedExts.add(PolicyMappings_Id.toString());
              supportedExts.add(PolicyConstraints_Id.toString());
              supportedExts.add(InhibitAnyPolicy_Id.toString());
              supportedExts = Collections.unmodifiableSet(supportedExts);
          }
          return supportedExts;
      }
docs: Gets an immutable Set of the OID strings for the extensions that
  the PKIXCertPathChecker supports (i.e. recognizes, is able to
  process), or null if no extensions are
  supported. All OID strings that a PKIXCertPathChecker might
  possibly be able to process should be included.
  
  @return the Set of extensions supported by this PKIXCertPathChecker,
  or null if no extensions are supported