[Insight Tracker] Click event without the category is not tracked

Steps to reproduce:

1. Open and run coffee insight tracker example
2. Clear the category filters ( "categories" : [])
3. Click on the button without the category set (Latte or Macchiato)
4. See the console 

Expected: All events should be tracked as there are no filters applied. 

Actual: Click events are not tracked.

Reproducibility:  100%

NOTE: To make it works we need to add  "categories" : [""], but it is inconsistent since there is no category set for mentioned buttons/events.