title: how to populate array of objects in mongoose that reference to another schema
body: <p>hello i went to populate all author with Course.</p>
  
  <pre><code> const courses = await Course.find().populate('author','name -_id');
      console.log(courses);
  
  const Author = mongoose.model('Author',mongoose.Schema({
      name:{
          type:String,
          required:true
      },
      bio:String,
      website:String
  }));
  
  const Course = mongoose.model('Course',mongoose.Schema({
      name:String,
      author:[{
          type: mongoose.Schema.Types.ObjectId,
          ref:'Author'
      }]
  }));
  </code></pre>
  
  <p>this is what i get:</p>
  
  <pre><code>[ { author: [ [Object], [Object] ],
      _id: 5cdc596bfd5a1e33e4833b2b,
      name: 'nodejs course',
      __v: 1 } ]
  </code></pre>
  
  <p>but i went to populate author name inside the author array 
  like this <code>[{author:[{name:'jhon'},{name:'jhon2'}],</code></p>
  
  <pre><code>[ { author: [ [Object], [Object] ],
      _id: 5cdc596bfd5a1e33e4833b2b,
      name: 'nodejs course',
      __v: 1 } ]
  </code></pre>