That makes sense, because your IG is not editable. So you don't have any column items, only cells. Once you make your IG an editable grid, it should work. For non-editable IG (and probably also for editable grids), you will need to check the underlying data in the model, which is conveniently passed in this.data

You can check with help of the js model api. Eg:

(this.data.selectedRecords.length && this.data.model.getValue(this.data.selectedRecords[0], 'DESCRIPTION') != "")

Notice upon selection change, there can be multiple rows selected depending on the IG configuration.