Counter of Groups in a Study

[Zarifa-nabil]

in one of the studies I ctreared, it gave me the total number of groups with +1. Going to Mongo DB we found that there is an extra group with null value. Removing this null from the DB the problem was solved. But we need to know how did this null showed as a group.
We tried to create new study with new groups and the total count of groups was correct.
But we still need to know how did this happen.