default <V extends @NonNull Object> V get(@NonNull CloudKeyHolder<V> keyHolder) {
        return this.get(keyHolder.key());
    }
Returns the value associated with the given {@code keyHolder} or fails exceptionally if it's missing.

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