code: public Attribute put(String attributeName) {
          Attribute attr = attributes.get(attributeName);
          if (attr == null) {
              attr = new Attribute();
          }
          attributes.put(attributeName, attr);
          return attr;
      }
docs: Add/update an attribute for this target.  Note that the attribute will have
  no configuration (empty configuration is created).  Returns the attribued added/updated
  @param attributeName
  @return Attribute