code: public Collection<? extends java.security.cert.Certificate>
              engineGenerateCertificates(InputStream is)
              throws CertificateException {
          if (is == null) {
              throw new CertificateException("Missing input stream");
          }
          try {
              return parseX509orPKCS7Cert(is);
          } catch (IOException ioe) {
              throw new CertificateException(ioe);
          }
      }
docs: Returns a (possibly empty) collection view of X.509 certificates read
  from the given input stream <code>is</code>.
  
  @param is the input stream with the certificates.
  
  @return a (possibly empty) collection view of X.509 certificate objects
  initialized with the data from the input stream.
  
  @exception CertificateException on parsing errors.