Fix monkey patch of ActiveRecord::Base for records without primary keys

Author: atranson-electra

CHANGELOG.md

@@ -12,6 +12,11 @@
 - Add official Rails 7.2 support. [#279](https://github.com/splitwise/super_diff/pull/279)
 - Add official Rails 8.0 support. [#281](https://github.com/splitwise/super_diff/pull/281)
 
+### Bug fixes
+
+- Fix `attributes_for_super_diff` (in monkey patch of `ActiveRecord::Base`) which would fail for classes that don't have a primary key.
+  ([#282](https://github.com/splitwise/super_diff/pull/282))
+
 ### Other changes
 
 - Fix `logger` dependency issues in CI. [#277](https://github.com/splitwise/super_diff/pull/277)

lib/super_diff/active_record/monkey_patches.rb

@@ -7,7 +7,7 @@ def attributes_for_super_diff
     id_attr = self.class.primary_key
 
     (attributes.keys.sort - [id_attr]).reduce(
-      { id_attr.to_sym => id }
+      id_attr.nil? ? {} : { id_attr.to_sym => id }
     ) { |hash, key| hash.merge(key.to_sym => attributes[key]) }
   end
 end