code: private void matchX509Certs(CertSelector selector,
          Collection<Certificate> matches) {
  
          for (Object obj : certSubjects.values()) {
              if (obj instanceof X509Certificate) {
                  X509Certificate cert = (X509Certificate)obj;
                  if (selector.match(cert)) {
                      matches.add(cert);
                  }
              } else {
                  // See certSubjects javadoc.
                  @SuppressWarnings("unchecked")
                  List<X509Certificate> list = (List<X509Certificate>)obj;
                  for (X509Certificate cert : list) {
                      if (selector.match(cert)) {
                          matches.add(cert);
                      }
                  }
              }
          }
      }
docs: Iterate through all the X509Certificates and add matches to the
  collection.