add meta field to search only if it is set
add meta field to search only if it is set

parisholley/wordpress-fantastic-elasticsearch,martybel/wordpress-fantastic-elasticsearch,innovatordm/wordpress-fantastic-elasticsearch,makeandship/wordpress-fantastic-elasticsearch,martybel/wordpress-fantastic-elasticsearch,innovatordm/wordpress-fantastic-elasticsearch,makeandship/wordpress-fantastic-elasticsearch,parisholley/wordpress-fantastic-elasticsearch,parisholley/wordpress-fantastic-elasticsearch,martybel/wordpress-fantastic-elasticsearch,innovatordm/wordpress-fantastic-elasticsearch,makeandship/wordpress-fantastic-elasticsearch