presto-main/src/main/java/io/prestosql/execution/QueryStateTimer.java/QueryStateTimer/toDateTime
class QueryStateTimer:    private Optional<DateTime> toDateTime(AtomicReference<Long> instantNanos)
    {
        Long nanos = instantNanos.get();
        if (nanos == null) {
            return Optional.empty();
        }
        return Optional.of(toDateTime(nanos));
    }