presto-main/src/main/java/io/prestosql/operator/LookupJoinOperator.java/JoinProcessor/outerJoinCurrentPosition
class JoinProcessor:        private boolean outerJoinCurrentPosition()
        {
            if (probeOnOuterSide && joinPosition < 0) {
                pageBuilder.appendNullForBuild(probe);
                if (tryBuildPage()) {
                    return false;
                }
            }
            return true;
        }