How to do a query on custom taxonomies that is uncategorised?

I have a custom taxonomy and I wish to do a query for all custom posts who has no value assigned for that taxonomy (i.e. uncategorised).

This is what I have so far:

  $uncatQuery = new WP_Query( array(
                'post_type'         =>  'course',
                'tax_query' => array (
                    array(
                        'taxonomy' => 'course_category',
                        'field' => 'name',
                        'terms' => '',
                    )
                )
            ) );

However this does not work.

Please help!

NOTE: I manage to get it to work by creating a query to get all tax ids and then use a NOT IN operator, but that requires an additional query.