M/Monit Error when adding hosts to group

[Former user]

I'm trying out M/Monit. I have 3 hosts set up and tried to create a group for them.

I created the group and when I try to add hosts to it (any of the 3 hosts, or all of them), I get this message :

Internal Server error: Failed to modify hostgroup id [-1] -- NumberFormatException: For input string undefined

It works fine if I first create the group, then exit the group screen and come back to add the hosts.

I think the problem is that when I first tried to add the hosts, the group had not actually been saved and didn't have an actual ID (-1 seems like a placeholder).