code: public static String get(String extension, String defaultCt) {
          final String mime = contentTypes.get(extension);
          return mime == null ? defaultCt : mime;
      }
docs: <p>get.</p>
  
  @param extension the extension
  @param defaultCt the content type to return if there is no known association for the specified extension
  @return the content type associated with <code>extension</code> or if no associate is found, returns
  <code>defaultCt</code>