Unable to register raster in temporal dataset (strds) in QGis Grass-toolbox

[eleemr]

Describe the bug

I want to create a dataset for a rain event with the first hour 70mm rain and the hours after that 0mm rain. Both are a seperate raster map. Adding these maps to a new temporal datasset should be possible in QGis GRASS-toolbox with the t.register module (like in GRASS GIS own GUI). When I try to register a raster I get the message trying this in QGis in the error 'ERROR: unit can only be set for relative time' (first screenshot). I noticed that it is not possible to leave the Time stamp unit empty (second screenshot).

To reproduce

Below describes the steps to take. In this case a mapset is already created and the rain raster are added to the mapset

1. In QGis go to plug-ins -> GRASS -> Open Grass Tools
2. Go to modules -> temporal -> Manage Datasets -> t. create and create a new temporal dataset
3. Go to modules -> temporal -> Manage maps in dataset -> t. register: this opens the panel like the 2nd screenshot
4. select the dataset
5. put in the name of a raster
6. click on 'advanced options'
7. fill in the start and end time like in 2nd screenshot
8. click on 'Run'

Expected behavior

When I do this in the GRASS GUI, the field for the time step unit can be blank and when I put in the rest of the values, the maps are registred without any problems or errors. In the QGis GRASS Toolbox there is always a value (yeaurs, months, days, hours, minutes, seconds) and no option for leaving it blank.

My expectation is that it will work if the option for the time stamp unit can be 'empty'.

Screenshots

System description

• Operating System: windows
• QGis: 3.40.5
• GRASS GIS version: 8.4.1

Additional context

I tried leaving the fields for the start and end time empty. And also checking the 'create an interval' option on and off. Then I got several other errors like 'The map has no timestamp and the start time is not set.' and 'maps and file are mutually exclusive'

[lrntct]

It seems to be a QGIS issue (how the GRASS tool is represented in QGIS), rather than a GRASS issue.

The related parser option in t.register clearly states that the time option is not required. So the QGIS interface should honour that.

[eleemr]

I think that during the development of the toolbox, the option to leave it empty was not included. In the parser, you can also see that the values for year, month, etc. are listed under the options. I think that’s why something is always filled in. Perhaps at the end, something like , , should be included in the list.