code: public static synchronized void unregister(final String serviceName,
                                                 final Callable<Class< ? >> factory) {
          if ( serviceName == null ) {
              throw new IllegalArgumentException( "serviceName cannot be null" );
          }
          if ( factories != null ) {
              List<Callable<Class< ? >>> l = factories.get( serviceName );
              if ( l != null ) {
                  l.remove( factory );
              }
          }
      }
docs: Removes the given service provider factory from the set of
  providers for the service.
  
  @param serviceName
  The fully qualified name of the service interface.
  @param factory
  A factory for creating a specific type of service
  provider. May be <tt>null</tt> in which case this
  method does nothing.
  @throws IllegalArgumentException if serviceName is <tt>null</tt>