Jena querybuilder clearWhereValues isn't working

Question

I want to clear the where clause values in a selectBuilder object, but I cannot get it work.

import org.apache.jena.arq.querybuilder.SelectBuilder;

public class TestClearWhere {
    public static void main(String[] args) {
        SelectBuilder sb = new SelectBuilder();
        sb.addVar("r").addVar("unit").addVar("time").addVar("value").addVar("interest");
        sb.addWhere("?r", "a", "sao:Point");
        System.out.println("Before clear\n" + sb.toString());
        sb.clearWhereValues(); // ?
        sb.clearValues(); // ? clearValues neither works
        System.out.println("After clear\n" + sb.buildString());
    }
}

Output

Before clear
SELECT  ?r ?unit ?time ?value ?interest
WHERE
  { ?r  a                     "sao:Point"}

After clear
SELECT  ?r ?unit ?time ?value ?interest
WHERE
  { ?r  a                     "sao:Point"}

Please let me know what I did wrong.