private boolean isNullConst(ExprNodeDesc exprNodeDesc) {
    //null constant could be typed so we need to check the value
    return exprNodeDesc instanceof ExprNodeConstantDesc && ((ExprNodeConstantDesc) exprNodeDesc).getValue() == null;
  }
Invoke special handling for expressions that can't be vectorized by regular
descriptor based lookup.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorizationContext.java