docs: protected ApplicationContext getApplicationContext(JobExecutionContext context)
              throws SchedulerException {
  
          final SchedulerContext schedulerContext = context.getScheduler().getContext();
          ApplicationContext applicationContext =  (ApplicationContext) schedulerContext.get(APPLICATION_CONTEXT_KEY);
  
          // show keys in context
          if(applicationContext==null) {
              logger.error(APPLICATION_CONTEXT_KEY+" is empty in "+ schedulerContext+":");
              if(schedulerContext.getKeys()!=null) {
                  for (String key : schedulerContext.getKeys()) {
                      Object value = schedulerContext.get(key);
                      String valueText = value!=null ? value.toString() : "<NULL>";
                      logger.info("    {} = {}", key, valueText);
                  }
              }
          }
  
          return applicationContext;
      }