code: private String getValue(String defaultValue, String attribute)
      {
          Check.notNull(attribute);
  
          if (root.hasAttribute(attribute))
          {
              return root.getAttribute(attribute);
          }
          return defaultValue;
      }
docs: Get the attribute value.
  
  @param defaultValue The value returned if attribute does not exist (can be <code>null</code>).
  @param attribute The attribute name (must not be <code>null</code>).
  @return The attribute value.
  @throws LionEngineException If attribute is not valid or does not exist.