title: How to filter fields from a mongo document with the official mongo-go-driver
body: <p>How can I filter fields with the mongo-go-driver. 
  Tried it with findopt.Projection but no success. </p>
  
  <pre><code>type fields struct {
      _id int16
  }
  
  s := bson.NewDocument()
  filter := bson.NewDocument(bson.EC.ObjectID("_id", starterId))
  
  var opts []findopt.One
  opts = append(opts, findopt.Projection(fields{
      _id: 0,
  }))
  
  staCon.collection.FindOne(nil, filter, opts...).Decode(s)
  </code></pre>
  
  <p>In the end, I want to suppress the field "_id". But the documents didn't change.</p>