Multi Editing constraint issue on Relation Reference

[signedav]

What is the bug or the crash?

Having a "Not null" constraint on a field.

Even though I have only valid values in the field represented by the Relation Reference, the Muli Edit Form is blocked, because it tells me, the Not NULL constraint is not fulfilled.

With text edit, it would accept the constraint:

It has nothing to do if the "Allow Null" setting is set or not on the Relation Reference Widget.

Steps to reproduce the issue

1. open testproject from provided gpkg
2. select multiple features of target_layer
3. open multi edit

simple.zip

Versions

Dev version on:

QGIS version	3.41.0-Master
QGIS code revision	9506122f60d
Libraries
Qt version	5.15.3
Python version	3.10.12
GDAL/OGR version	3.9.0dev-365401613a
PROJ version	8.2.1
EPSG Registry database version	v10.041 (2021-12-03)
GEOS version	3.10.2-CAPI-1.16.0
SQLite version	3.37.2
PDAL version	2.3.0
PostgreSQL client version	17.0 (Ubuntu 17.0-1.pgdg22.04+1)
SpatiaLite version	5.0.1
QWT version	6.1.4
QScintilla2 version	2.11.6
OS version	Ubuntu 22.04.5 LTS
This copy of QGIS writes debugging output.
Active Python plugins
toggle_labels_widget	1.0.2
plugin_reloader	0.9.3
layer_grid_view	0.1
QgisModelBaker	dev
changeDataSource	3.1
processing	2.12.99
db_manager	0.1.20

And 3.40.0

Supported QGIS version

• I'm running a supported QGIS version according to the roadmap.

New profile

• I tried with a new QGIS profile

Additional context

No response

[signedav]

This concerns the multi edit you open via the toolbar. The one in the attribute table behaves differently wrong. It does not block the form by the constraint, but instead it displays the widget-default but does not apply it. But this is another issue.