TypeError singleton can't be dumped

Question

I am working on a Rails 4 project and using readthis_store gem to do my caching. I do have the following code though

I have user model with a method block_reason

class User < ActiveRecord::Base

  def block_reason
    Rails.cache.fetch([self.cache_key, __method__], expires_in: 1.hours) do
      {
          blocked: true,
          blocked_reason: reason,
          blocked_reason_text: reason_text,
          application_blocks: {
            status: self..status,
            name_check: self.name_check,
            id_check: self.id_check,
          }
       }
    end
  end
end

In my controller, i have the following method index which calls the block_reason method

class Private::V1::JobsController < Private::V1::ApiController
  def index
    response = @current_user.block_reason.try(:to_h)

    json_success(nil, response)
  end
end

But when i make the APi call, i get the error

TypeError: singleton can't be dumped
  from readthis/entity.rb:50:in `dump'
  from readthis/entity.rb:50:in `dump'
  from readthis/cache.rb:315:in `write_entity'
  from readthis/cache.rb:86:in `block in write'
  from connection_pool.rb:63:in `block (2 levels) in with'
  from connection_pool.rb:62:in `handle_interrupt'
  from connection_pool.rb:62:in `block in with'
  from connection_pool.rb:59:in `handle_interrupt'
  from connection_pool.rb:59:in `with'
  from readthis/cache.rb:346:in `block in invoke'
  from readthis/cache.rb:338:in `block in instrument'
  from active_support/notifications.rb:166:in `instrument'
  from readthis/cache.rb:338:in `instrument'
  from readthis/cache.rb:345:in `invoke'
  from readthis/cache.rb:85:in `write'
  from readthis/cache.rb:146:in `fetch'

I know the error is happening in the readthis_store gem and has something to do with Marshal.dump defining the object cached as a singleton.

But i do not know how else to solve this issue. I have tried various options but all to no avail.

Not sure if anyone has come across this and been able to solve it on Rails 4.