Meeting cannot be null error when creating Group if Center hierarchy disabled

If Center hierarchy is turned off, user encounters an exception if creating a group without a meeting schedule defined.

repro steps:
1. set custom property:
ClientRules.CenterHierarchyExists=false
2. Start Mifos, and click on Create Group.
3. pick a branch office. On create group page, pick Group Name, recruited by, then Preview (don't pick Meeting schedule)
4. Submit

actual result: exception - (See attached screenshot)

expected result: able to create group without meeting.