Introduction
------------

1. The foreign key was not explicitly specified on the association.
2. The `AbuseReport` model contains two references to user - `reporter_id` and
   `user_id`
3. `user.abuse_report` is supposed to return the single abuse report where
   `user_id` refers to the given user.

Bug Description
---------------

1. `user.abuse_report` would return an abuse report where `reporter_id` referred
   to the current user, if such an abuse report was present.

2. This implies a slightly more serious bug as well:

   - Assume User A filed an abuse report against User B
   - We have an abuse report where `reporter_id` is User A and `user_id` is User B
   - If User A is updated (`user_a.block`, for example), the abuse report would
     also be updated, such that both `reporter_id` _and_ `user_id` point to User A.

Fix
---

Explicitly declare the foreign key `user_id` in the `has_one` declaration