presto-main/src/main/java/io/prestosql/operator/LookupJoinPageBuilder.java/LookupJoinPageBuilder/appendNullForBuild
class LookupJoinPageBuilder:    public void appendNullForBuild(JoinProbe probe)
    {
        // probe side
        appendProbeIndex(probe);

        // build side
        buildPageBuilder.declarePosition();
        for (int i = 0; i < buildOutputChannelCount; i++) {
            buildPageBuilder.getBlockBuilder(i).appendNull();
        }
    }