Bug report #18638
Clearing a data-defined replaces expression by 'null' text instead of being empty
|Affected QGIS version:||3.1(master)||Regression?:||Yes|
|Operating System:||Easy fix?:||No|
|Pull Request or Patch supplied:||No||Resolution:|
|Crashes QGIS or corrupts data:||No||Copied to github as #:||26526|
Add a data-defined expression to a layout picture item (i was there when i found the issue but should be the same for all DD buttons).
Now click the DD button and select Clear
Again select the DD button, Edit
The expression builder is filled with a NULL text you need to erase before writing the new expression.
It would be better to have the widget empty, as it's in 2.18.
Don't set cleared data defined properties to NULL in expression editor