code: public String getExtensionsAsString() {
          String extensionsList = null;
          if (extensions != null) {
              StringBuilder sb = new StringBuilder();
              for (String key : extensions.keySet()) {
                  sb.append(key);
                  sb.append("; ");
              }
              extensionsList = sb.toString().trim();
          }
          return extensionsList;
      }
docs: Returns the extensions list as a comma separated string as specified by the rfc.
  
  @return extension list string or null if no extensions are enabled