docs: public static synchronized Class< ? > locate(final String serviceName) {
          if ( serviceName == null ) {
              throw new IllegalArgumentException( "serviceName cannot be null" );
          }
          if ( factories != null ) {
              List<Callable<Class< ? >>> l = factories.get( serviceName );
              if ( l != null && !l.isEmpty() ) {
                  Callable<Class< ? >> c = l.get( l.size() - 1 );
                  try {
                      return c.call();
                  } catch ( Exception e ) {
                  }
              }
          }
          return null;
      }