fix reference

pkg/references/reference.go

@@ -14,8 +14,8 @@ type Reference struct {
 
 func (r *Reference) MarshalBSON() ([]byte, error) {
 	d := bson.D{
-		{"id", r.ID},
-		{"collection_id", r.CollectionID},
+		{Key: "id", Value: r.ID},
+		{Key: "collection_id", Value: r.CollectionID},
 	}
 
 	if r.Disabled {
@@ -99,5 +99,4 @@ func (r *Reference) Fetch(i interface{}) interface{} {
 	default:
 		panic("unknown parameter")
 	}
-	return nil
 }