@Override
  public String vectorExpressionParameters() {
    return getColumnParamString(0, inputColumnNum[0]) + ", " + getColumnParamString(1, inputColumnNum[1]) +
        ", null";
  }
Do conditional execution of the THEN vector expression with NULL ELSE of a SQL IF statement.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/IfExprCondExprNull.java