Issue with active_record.marshalling_format_version = 7.1

[JerrodCarpenter]

As noted in this PR comment, it looks like there's an issue where the memo wise hash is sometimes not caught when using this new marshalling format version.

  Rails.application.config.active_record.marshalling_format_version = 7.1

This surfaces as NoMethodError: undefined method 'fetch' for nil

I've observed this behavior on version 1.7 and 1.10

[JerrodCarpenter]

What's happening here is the new format for caching does not cache instance variables for active record objects. Thus the memo wise instance variable is nil and we see our NoMethodError. The Rails team discourages the caching of AR objects. However, it's been effective tool for our team. In our project we added some custom marshalling code to ensure the memo wise instance variable is cached and loaded from the cache appropriately. Anyways, closing this issue, as I think this is actually a weird side effect of Rails changing behavior and not a bug.

[JacobEvelyn]

Thanks for the update @JerrodCarpenter !