There is an infinite loop happening when we try to cache a Mongoid model instance. 

Steps to Reproduce 👣

1. Setup a simple Mongoid Class

class Project
  include Mongoid::Document
  
  field :name, type: String
end
 

2. Try to cache that model instance

project = Project.new(name: 'Oi')
Rails.cache.fetch(project) 

3. An infinite loop happens, raising the SystemStackError exception, as we can see below