failure property Null safety

1. baguette
2. CheckoutSecurity
3. CheckoutSecurity
4. failure property

CheckoutSecurity class

1. Constructors
2. CheckoutSecurity
3. Properties
4. failure
5. hashCode
6. runtimeType
7. success
8. uri
9. Methods
10. noSuchMethod
11. toString
12. Operators
13. operator ==