Service subscription with blank plan throws weird 404 page

Step to reproduce:
1. Create user and application
2. Create at least 2 services
3. Go to Accounts->Listing and choose created account
4. Go to Service Subscriptions tab and try to add one available service subscription
5. In Modal window leave plan blank and press Create subscription

Current:
6. 404 page and background page frontend is "weird"

Expected:
6. Don't allow choose blank option in Subscription's plan