code: public PrimaryKey addComponent(String keyAttributeName, Object keyAttributeValue) {
          components.put(keyAttributeName,
              new KeyAttribute(keyAttributeName, keyAttributeValue));
          return this;
      }
docs: Add a key component to this primary key.
  
  Note adding a key component with the same name as that of an existing
  one would overwrite and become a single key component instead of two.