code: @SuppressWarnings("unchecked")
      private <T extends Assignable> Class<T> loadExtensionClass(String extensionClassName) {
          try {
              return (Class<T>) ClassLoaderSearchUtilDelegator.findClassFromClassLoaders(extensionClassName,
                  getClassLoaders());
          } catch (final ClassNotFoundException e) {
              throw new RuntimeException("Could not load class " + extensionClassName, e);
          }
      }
docs: Delegates class loading of <code>extensionClassName</code> to
  {@link ClassLoaderSearchUtilDelegator#findClassFromClassLoaders(String, Iterable)} passing the
  <code>extensionClassName</code> and the instance's <code>classLoaders</code>.
  
  @param <T>
  @param extensionClassName
  @return