Thanks, I was running 3.0. I was lucky :)
```ruby
  def accessible_environments
    (KTEnvironment.content_readable(current_organization).all +
        KTEnvironment.changesets_readable(current_organization).all.map { |env| env.prior if env.prior }.compact).
        uniq
  end
```
works fine. Problem was that `KTEnvironment.content_readable(current_organization)` is relation not an array. Calling `#<<` on it would made weird stuff so converting it to `Array` with `#all` helps.