code: public void writeString(String attribute, String content)
      {
          if (content == null)
          {
              write(attribute, NULL);
          }
          else
          {
              write(attribute, content);
          }
      }
docs: Write a string. If the content is equal to <code>null</code>, {@link #NULL} is wrote instead.
  
  @param attribute The attribute name (must not be <code>null</code>).
  @param content The string value (can be <code>null</code>).
  @throws LionEngineException If error when writing.