code: private Document findAssociation(AssociationKey key, AssociationContext associationContext, AssociationStorageStrategy storageStrategy) {
  		final Document associationKeyObject = associationKeyToObject( key, storageStrategy );
  		MongoCollection<Document> associationCollection = getAssociationCollection( key, storageStrategy, associationContext );
  
  		FindIterable<Document> fi = associationCollection.find( associationKeyObject );
  		return fi != null ? ( fi.projection( getProjection( key, false ) ).first() ) : null ;
  	}
docs: not for embedded