docs: @Override
      public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)
              throws BeansException {
          if (propertyResolver == null) {
              try {
                  MutablePropertySources sources = new MutablePropertySources();
                  PropertySource<?> localPropertySource =
                          new PropertiesPropertySource(EXTENDED_PROPERTIES_SOURCE, mergeProperties());
                  sources.addLast(localPropertySource);
  
                  propertyResolver = new PropertySourcesPropertyResolver(sources);
  
              } catch (IOException e) {
                  throw new BeanInitializationException("Could not load properties", e);
              }
          }
  
          super.postProcessBeanFactory(beanFactory);
      }