I’m trying out Piklist and so far it’s really great!

Currently i try to add relationships to custom-post-types as well as users.

So i need to add a field to the user where administrators can select none or one entry from a custom-post-type.
This is what i have/found and added to the parts/users-folder.
So far it works, but i can not select an emtpy option, i always have to select an existing post.
Is it possible to add an emtpy option to the top of the list?
how would i do that?

piklist('field', array(
    'type' => 'select'
    , 'field' => 'current_selection'
    , 'label' => __('Current Selection')
    , 'description' => __('Currently selected Post')
    , 'attributes' => array(
        'class' => 'text'
    )
    , 'choices' => piklist(            
        get_posts(array(
            'post_type' => 'my-custom-post-type',
            'numberposts' => -1,
            'orderby' => 'title',
            'order' => 'ASC'
        )), array('ID', 'post_title')
    ),
));