mysql join query with sum retuns null

If article_payments table is null the query returns null. How shoul i set the query yo get recors if doesnt exist in SUM(payment_total) like 0.00 ?

SELECT article_name,user_real_name,user_name,SUM(`article_payment`) as holding,paid
 FROM article_articles AS t1
 JOIN article_users ON (t1.article_name=article_users.user_id) 
 JOIN (SELECT user_id,SUM(`payment_total`) as paid FROM article_payments GROUP BY user_id) AS t2 ON (t1.article_name=t2.user_id)
 GROUP BY t2.user_id
 

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