Strange labels for NULL values of attributes with value map form widget

Nobody has claimed this yet.

Whenever you have a value map for a field defined in the form that includes the NULL value and you set a non-NULL value first and then try to set it to NULL, if you have a label based on that field you would get that strange string as shown below instead of an empty string.


This happens only when modifying a feature in MM Input - in QGIS, when the value-mapped field is modified to NULL the label is empty, as expected.

I have created a simple public project to replicate and test the issue:
https://app.merginmaps.com/projects/rpasiok/test_value_map_labels/tree

MM Input version: 1.7.0 on Android 10

Start with the public test project at https://app.merginmaps.com/projects/rpasiok/test_value_map_labels/tree and reproduce the value-map NULL transition in MM Input on Android 10. Compare the result with QGIS, where the label is empty; done means modifying a feature from a non-NULL value to NULL no longer displays the strange string.

Written by the indexing model from the issue text.