title: Loop custom array from mongoose returned empty
body: <p>here is my problem</p>
  <p>I want to loop data from two entities <code>Project</code> and <code>User</code>, my <code>Project</code> entity have a field with <code>User</code> id called creatorId.</p>
  <p>I looped it and tried to add my user data <code>_id</code>, <code>displayname</code> and <code>avatarUrl</code>.</p>
  <p>For now that work, but when I send it from the backend to the frontend nothing appears, like the array is empty.</p>
  <pre><code>const projectList = [];
    Project.find({}, function(err, projects) {
       projects.map(project =&gt; {
        User.findById(project.creatorId, function(err, creator){
          projectList.push({
            _id: project._id,
            title: project.title,
            description: project.description,
            avatarUrl: project.avatarUrl,
            creationDate: project.creationDate,
            projectCreator: {
              _id: creator._id,
              displayname: creator.displayname,
              avatarUrl: creator.avatarUrl
            },
            git: project.git
          })
        })
      })
    });
    res.send(projectList);  
  
  </code></pre>