default <V extends @NonNull Object> @NonNull Optional<V> optional(@NonNull CloudKeyHolder<V> keyHolder) {
        return this.optional(keyHolder.key());
    }
Returns the value associated with the given {@code keyHolder}.

@param <V>       the type of the value
@param keyHolder the holder of the key
@return the value
cloud-core/src/main/java/org/incendo/cloud/key/CloudKeyContainer.java