Value maps have been set for some attributes in the properties of a layer (which is an offline edit of a PostGIS database saved as a spatialite file).
But in the drop down selection it does not allow for a Null to be selected. So if a user selects one of them, there is no way to undo the selection.
I have tried entering both Null, and NULL, into the value map, and having an extra blank row.
The extra blank row does give me a blank option,
but the value in the field is '' rather than NULL.
And selecting NULL gives me 'NULL' with the single quotation marks
In response to answer Bhaskar
When I run this SELECT query, I would like to have just these 4 values
How can set it up so that a user can essentially deselect a value and return it to its previous NULL state?
I have tried to run the SQL suggested by Bhaskar to just swap out a inserted NULL through the value map.
INSERT INTO awrtracker.awr_tracker_sync (threat_lvl) VALUES (NULL) where threat_lvl is 'NULL';
In place of the final 'NULL' in the expression I have tries 'Null' and 'null'. But the error is the same "ERROR: syntax error at or near "where".
It's an SQL problem isn't it, from what I have researched the WHERE statement is invalid here for PostgreSQL?