Trailblazer: Uninitialized constant Thing::Update (contract.rb:5)

contract.rb

class Thing::Create::Contract < Reform::Form
  ...
end

class Thing::Update::Contract < Thing::Create::Contract
  ...
end

crud.rb

class Thing < ActiveRecord::Base
  class Create < Trailblazer::Operation
    include Model
    model Thing, :create

    require_dependency 'thing/contract'
    self.contract_class = Contract
    contract_class.model Thing

    def process(params)
      ...
    end
  end

  class Update < Create
    action :update
    
    def process(params)
      ...
    end
  end
end