presto-main/src/main/java/io/prestosql/operator/SpatialJoinOperator.java/SpatialJoinOperator/getOutput
class SpatialJoinOperator:    @Override
    public Page getOutput()
    {
        verify(!finished);
        if (!pageBuilder.isFull() && probe != null) {
            processProbe();
        }

        if (pageBuilder.isFull()) {
            Page page = pageBuilder.build();
            pageBuilder.reset();
            return page;
        }

        if (finishing && probe == null) {
            Page page = null;
            if (!pageBuilder.isEmpty()) {
                page = pageBuilder.build();
                pageBuilder.reset();
            }
            finished = true;
            close();
            return page;
        }

        return null;
    }