rails namespace belongs_to

Tenho o seguinte configuração

module  Account
  class Permission < ApplicationRecord
  end
end

module Account
  class GroupPermission < ApplicationRecord
    belongs_to :permission
  end
end

Table:  account_group_users

account_users_id bigint,

account_groups_id bigint,

Table:  account_group_permissions

account_permissions_id bigint,

account_groups_id bigint,

Quando tento acessar  a instancia Account::GroupPermission  e por ela acessar Account::Permission  retorna nil.

Só funciona se eu especificar o class_name: