fix: handle nil paginated in fetch_upcoming_events and fetch_past_events

[mroderick]

Summary

• Fixes NoMethodError: undefined method 'group_by' for nil when /events/upcoming or /events/past is accessed with no events or an out-of-bounds page number

Root Cause

In EventsController#fetch_upcoming_events and fetch_past_events, the code collects events from Workshops, Meetings, and Events, sorts them, and then calls pagy to paginate. However:

1. When sorted is empty (no upcoming/past events), paginated can be nil
2. When requesting an out-of-bounds page (e.g., page 3 when only 2 pages exist), paginated can also be nil

The code then calls paginated.group_by(&:date) without checking for nil, causing the error.

Changes

1. Added early return [{}, nil] when no events exist to avoid unnecessary pagination
2. Added paginated ||= [] guard clause to handle edge cases where paginated is nil even with events

Testing

• Added spec/controllers/events_controller_spec.rb with tests for empty events edge case
• All existing tests continue to pass

Rollbar Reference

https://app.rollbar.com/a/codebar-production/fix/item/codebar-production/669#detail