code: public static String getExtension(final String pMIME) {
          String mime = bareMIME(StringUtil.toLowerCase(pMIME));
          List<String> extensions = sMIMEToExt.get(mime);
          return (extensions == null || extensions.isEmpty()) ? null : extensions.get(0);
      }
docs: Returns the default file extension for the given MIME type.
  Specifying a wildcard type will return {@code null}.
  
  @param pMIME the MIME type
  
  @return a {@code String} containing the file extension, or {@code null}
  if there are no known file extensions for the given MIME type.