Bug: TDEngine Version 3.3.4.8 - range fill(prev) Yields Output with Invalid Characters

[mesquita]

Bug Description

We are having an issue when querying the database using range combined with fill(prev) where the end range timestamp extends beyond the last occurrence of a tag sample.

When trying to make a query like this:

select _irowts as `time`,
    `tag`,
    interp(`value`) as `value`
from sensors
where `tag` in ('ABC.PV')
partition by tbname
range('2024-12-01 00:00:00', '2025-01-01 00:00:00') every(600s) fill(prev);

the current output in this version has for the output tag the following value:

ABC.��

Instead of returning the expected value ABC.PV, the tag field contains invalid characters such as \x00\x00 when the query includes a “future” value (i.e., a timestamp after the last sample for the tag).

To Reproduce

1. Run a query similar to the example above.
2. Ensure the range includes an end timestamp beyond the last known sample for the tag.

Expected Behavior
The output should correctly display ABC.PV for the tag field if the interpolation value (interp) is correctly computed.

Screenshots

Environment (please complete the following information):
TDEngine version 3.3.4.8

Thank you very much!