code: public static <A> Lens.Simple<HMap, Maybe<A>> valueAt(TypeSafeKey<?, A> key) {
          return simpleLens(m -> m.get(key), (m, maybeA) -> maybeA.fmap(a -> m.put(key, a)).orElseGet(() -> m.remove(key)));
      }
docs: A lens that focuses on a value at a {@link TypeSafeKey.Simple}&lt;A&gt; in an {@link HMap}, as a {@link Maybe}.
  
  @param key the key
  @param <A> the value type at the key
  @return the lens