@Override
  public VectorExpressionDescriptor.Descriptor getDescriptor() {
    return (new VectorExpressionDescriptor.Builder())
        .setMode(
            VectorExpressionDescriptor.Mode.PROJECTION)
        .setNumArguments(2)
        .setArgumentTypes(
            VectorExpressionDescriptor.ArgumentType.getType("long"),
            VectorExpressionDescriptor.ArgumentType.getType("long"))
        .setInputExpressionTypes(
            VectorExpressionDescriptor.InputExpressionType.NULLSCALAR,
            VectorExpressionDescriptor.InputExpressionType.COLUMN).build();
  }
This class performs constant OR column expression where the constant is null
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/ScalarNullOrCol.java