code: public Extension findExtension(String keyStr) throws RuntimeFault, RemoteException {
          if (keyStr == null) {
              throw new NullPointerException();
          }
          return getVimService().findExtension(getMOR(), keyStr);
      }
docs: Find the extension based on the unique key of the plugin If
  <code>keyStr</code> is null then a <code>NullPointerException</code>
  
  @param keyStr The unique key for the plugin
  @return The extension object found with the unique key
  @throws RemoteException
  @throws RuntimeFault
  @throws RemoteException if something is wrong with web service call, either because of
  the web service itself, or because of the service provider unable
  to handle the request.