code: public String identifierToSuppressionId(Identifier id) {
          if (id instanceof PurlIdentifier) {
              final PurlIdentifier purl = (PurlIdentifier) id;
              return purl.toGav();
          } else if (id instanceof CpeIdentifier) {
              try {
                  final CpeIdentifier cpeId = (CpeIdentifier) id;
                  final Cpe cpe = cpeId.getCpe();
                  return String.format("cpe:/%s:%s:%s", Convert.wellFormedToCpeUri(cpe.getPart()),
                          Convert.wellFormedToCpeUri(cpe.getWellFormedVendor()),
                          Convert.wellFormedToCpeUri(cpe.getWellFormedProduct()));
              } catch (CpeEncodingException ex) {
                  LOGGER.debug("Unable to convert to cpe URI", ex);
              }
          } else if (id instanceof GenericIdentifier) {
              return id.getValue();
          }
          return null;
      }
docs: Converts an identifier into the Suppression string when possible.
  
  @param id the Identifier to format
  @return the formatted suppression string when possible; otherwise
  <code>null</code>.