Modify get_districts_at_version to only return non-empty districts
Modify get_districts_at_version to only return non-empty districts

The Unassigned district is still returned

JimCallahanOrlando/DistrictBuilder,JimCallahanOrlando/DistrictBuilder,JimCallahanOrlando/DistrictBuilder,JimCallahanOrlando/DistrictBuilder