code: package it.unibz.inf.ontop.iq.node;
  
  import it.unibz.inf.ontop.iq.LeafIQTree;
  import it.unibz.inf.ontop.iq.exception.QueryNodeTransformationException;
  import it.unibz.inf.ontop.iq.transform.node.HomogeneousQueryNodeTransformer;
  
  /**
   * Temporary QueryNode that says that replace a non-satisfied sub-tree.
   *
   * Is expected to remove quickly.
   *
   * See IntermediateQueryFactory for creating a new instance.
   */
  public interface EmptyNode extends LeafIQTree {
      @Override
      EmptyNode acceptNodeTransformer(HomogeneousQueryNodeTransformer transformer)
              throws QueryNodeTransformationException;
  }
  