docs: improve optional and nillable context examples

Author: palkan

docs/authorization_context.md

@@ -18,8 +18,26 @@ end
 
 Now you must provide `account` during policy initialization. When authorization key is missing or equals to `nil`, `ActionPolicy::AuthorizationContextMissing` error is raised.
 
-**NOTE:** if you want to allow passing `nil` as `account` value, you must add `allow_nil: true` option to `authorize`.
-If you want to be able not to pass `account` at all, you must add `optional: true`
+If you want to allow passing `nil` as `account` value, you must add `allow_nil: true` option to `authorize`.
+If you want to be able not to pass `account` at all, you must add `optional: true`:
+
+```ruby
+class GuestPolicy < ApplicationPolicy
+  # With allow_nil: true, the `user` key is still required to be present
+  # in the authorization context
+  authorize :user, allow_nil: true
+end
+
+class ProjectPolicy < ApplicationPolicy
+  # With optional: true, authorization context may not include the `user` key at all
+  authorize :team, optional: true
+end
+
+GuestPolicy.new(user: nil) #=> OK
+GuestPolicy.new #=> raises ActionPolicy::AuthorizationContextMissing
+
+ProjectPolicy.new(user: user) #=> OK
+```
 
 To do that automatically in your `authorize!` and `allowed_to?` calls, you must also configure authorization context. For example, in your controller:
 

lefthook.yml

@@ -15,4 +15,4 @@ pre-commit:
     rubocop:
       tags: style
       glob: "**/*.md"
-      run: BUNDLE_GEMFILE=gemfiles/rubocop.gemfile bundle exec rubocop {staged_files}
+      run: BUNDLE_GEMFILE=gemfiles/rubocop.gemfile bundle exec rubocop -c .rubocop-md.yml {staged_files}