code: public static Digest valueOf(final String value) {
          final String[] parts = value.split("=", 2);
          if (parts.length == 2) {
              return new Digest(parts[0], parts[1]);
          }
          return null;
      }
docs: Get a Digest object from a string-based header value
  @param value the header value
  @return a Digest object or null if the value is invalid