code: protected final DelegateClassLoader createClassLoader(PluginSource source,
              ClassLoader parent) {
          final Stream<URL> urls = Require.nonNullResult(source.getPluginURLs(),
                  "pluginSource.getPluginURLs");
          return DelegateClassLoader.forPlugins(urls, parent);
      }
docs: Creates a {@link ClassLoader} which accesses the given collection of
  plugins.
  
  @param source The plugins.
  @param parent The parent ClassLoader.
  @return The created ClassLoader.