code: protected final TagAttribute getRequiredAttribute(String localName) throws TagException
      {
          TagAttribute attr = this.getAttribute(localName);
          if (attr == null)
          {
              throw new TagException(this.tag, "Attribute '" + localName + "' is required");
          }
          
          return attr;
      }
docs: Utility method for fetching a required TagAttribute
  
  @param localName
  name of the attribute
  @return TagAttribute if found, otherwise error
  @throws TagException
  if the attribute was not found