code: public String convertExtensionToMediaType(String extension) {
          ProvFormat format = extensionRevMap.get(extension);
          if (format == null)
              return null;
          return mimeTypeMap.get(format);
      }
docs: Maps an file extension to a Media type
  @param extension the extension of a file containing a serialization of PROV
  @return a String for the Internet Media type corresponding to a file with this extension