I've just created cartogram using styles/graduated symbol. But there are some missing elements on the map. Objects without data in attribute table are not present on the map (NULL in corresponding column in Attibute table). I was able to show such objects on the map using 0.0-0.0 interval in previous versions of QGIS. It does nothing now, just showing objects with 0 value but NULL objects are still missing. How to display them to make my map complete?
Grey countries with 0 value, white spaces (e.g. South Sudan) while NULL is in the column.
