code: public static <S> Key<S> from(String key, Class<? extends S> valueClass)
      {
          return new Key<S>(key, valueClass);
      }
docs: Creates a new Key with the given key string and value class.
  
  @param key        the key string representing this Key
  @param valueClass the class of the value associated with this Key
  @return a new Key with the given key string and value class