code: private void initMessageSource() {
          if (contextBeanRegistry.containsBean(MESSAGE_SOURCE_BEAN_ID)) {
              messageSource = contextBeanRegistry.getBean(MESSAGE_SOURCE_BEAN_ID, MessageSource.class);
              if (log.isDebugEnabled()) {
                  log.debug("Using MessageSource [" + messageSource + "]");
              }
          } else {
              // Use empty MessageSource to be able to accept getMessage calls.
              messageSource = new DelegatingMessageSource();
              if (log.isDebugEnabled()) {
                  log.debug("Unable to locate MessageSource with name '" + MESSAGE_SOURCE_BEAN_ID +
                          "': using default [" + messageSource + "]");
              }
          }
      }
docs: Initialize the MessageSource.
  Use parent's if none defined in this context.