@Override
    public Object process(Node nd, Stack<Node> stack, NodeProcessorCtx procCtx,
        Object... nodeOutputs) throws SemanticException {
      assert (nd instanceof ExprNodeConstantDesc || nd instanceof ExprDynamicParamDesc);

      // Create a dependency that has no basecols
      Dependency dep = new Dependency();
      dep.setType(LineageInfo.DependencyType.SIMPLE);
      dep.setBaseCols(new LinkedHashSet<BaseColumnInfo>());

      return dep;
    }
Processor for constants and null expressions. For such expressions the
processor simply returns a null dependency vector.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/lineage/ExprProcFactory.java