title: Return Map Row NULL
body: <p>I'm trying to map a json response from mysql query, but i receive ho response: <code>data: NULL</code></p>
  
  <p>This is my code:</p>
  
  <pre><code>const audience = rows.map((row) =&gt; {
      db.query(CountAudiences, [row.campaign], function(err, count, fields) {
          if (err) throw err;
          console.log('Query result: ', count[0].audience);
          return {
              id: row.id,
              title: row.title,
              campaign: row.campaign,
              action: row.action,
              date: row.date,
              audiences: count[0].audience
          }
      });
  });
  res.json({
      count: rows.length,
      data: audience
  })
  </code></pre>
  
  <p>Response:</p>
  
  <pre><code>{
     "count":1,
     "data":[
        null
     ]
  }
  </code></pre>
  
  <p>Do you know how solve this?
  Thanks :)</p>