code: private String getKeyPrefix(Class targetClass) {
  
          String prefix = ((ConfigBundle) targetClass.getAnnotation(ConfigBundle.class)).value();
  
          if (prefix.isEmpty()) {
              prefix = StringUtils.camelCaseToHyphenCase(targetClass.getSimpleName());
          }
  
          if (".".equals(prefix)) {
              prefix = "";
          }
  
          return prefix;
      }
docs: Generate a key prefix from annotation, class name, or parent prefix in case of nested classes.
  
  @param targetClass target class
  @return key prefix