code: protected static final <T, K extends Serializable>
      List<K> _keys2Ids(
                      final Collection<Key<T>> keys
                      )
      {
          List<K>  ids = new ArrayList<K>();
          if (keys != null ) {
              for (Key<T>  key : keys) {
                  @SuppressWarnings( "unchecked" )
                  K  id = (K)key.getId();
                  ids.add( id );
              }
          }
  
          return ids;
      }
docs: Converts Morphia Key<T> list to K, i.e. "_id", list.
  
  @throws  OvalRepositoryException