@Override
  public VectorExpressionDescriptor.Descriptor getDescriptor() {
    return (new VectorExpressionDescriptor.Builder())
        .setMode(
            VectorExpressionDescriptor.Mode.PROJECTION)
        .setNumArguments(1)
        .setArgumentTypes(
            VectorExpressionDescriptor.ArgumentType.ALL_FAMILY)
        .setInputExpressionTypes(
            VectorExpressionDescriptor.InputExpressionType.COLUMN).build();
  }
This expression evaluates to true if the given input columns is not null.
The boolean output is stored in the specified output column.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/IsNotNull.java