QGIS » QGIS Application

When a vector layer is classified using the categorized style on numeric fields with NULL values, unchecking the blank/NULL class (using shapefiles) or the "0" class (using other data formats) makes also the features of the other classes invisible.

Steps to replicate the issue:
- create a shapefile layer with a numeric (integer or real) field named A
- start editing
- add three features: the first with A=1, the second with A=2 and the third with A=NULL (no value)
- save and stop editing
- open the Vector Properties Dialog - Style tab (don't use the Layer Styling Dock)
- classify the layer using the categorized style on the field A: the classes "0", "1", "2" and "blank" are automatically created
- uncheck or remove the class "blank": all the features of the layer disappear
- uncheck or remove the class "0": the other checkboxes return to work properly

Using PostGIS, SpatiaLite or GeoPackage layers the behavior is slightly different. The "blank" checkbox works properly but unchecking the class "0" the features of the classes "1" and "2" disappear.

The issue doesn't occur:
- using the Layer Styling Dock
- saving and reopening the project with the style already set

The issue is OS independent and also occurs in QGIS 2.14.20 and QGIS 2.18.14.