@Override
  public String vectorExpressionParameters() {
    // Second input parameter but 3rd column.
    return getColumnParamString(0, inputColumnNum[0]) + ", null, " + getColumnParamString(2, inputColumnNum[1]);
  }
Do conditional execution of a NULL THEN and a ELSE vector expression of a SQL IF statement.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/IfExprNullCondExpr.java