```ruby
class CouponDecorator < ApplicationDecorator
  decorates :coupon

  def percent_off
    "#{coupon.percent_off}% Off"
  end

  def expiration
    coupon.redeem_by.strftime("%Y-%m-%d")
  end

  def applicable_plans
    coupon.subscription_plans.map {|p| p.name}.join(',')
  end
end```

Fix to coupon decorator. Don't assume we have an expiration. Need test coverage on coupon decorator.
user
```ruby
class CouponDecorator < ApplicationDecorator
  decorates :coupon

  def percent_off
    "#{coupon.percent_off}% Off"
  end

  def expiration
    if coupon.redeem_by?
      coupon.redeem_by.strftime("%Y-%m-%d")
    else
      'No expiration'
    end
  end

  def applicable_plans
    coupon.subscription_plans.map {|p| p.name}.join(',')
  end
end```
assistant