@Override
    public <V> TransformingRequestPreparation<T, R> attr(AttributeKey<V> key, @Nullable V value) {
        delegate.attr(key, value);
        return this;
    }
Sets the specified {@link ResponseAs} that converts the {@code T} type object into another.
core/src/main/java/com/linecorp/armeria/client/TransformingRequestPreparation.java