Validator constructor Null safety

1. diginote
2. input_validators
3. Validator
4. Validator constructor

Validator class

1. Constructors
2. Validator
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. noSuchMethod
8. toString
9. Operators
10. operator ==
11. Static methods
12. isEmpty
13. isValidEmail
14. isValidPairingCodeFormat
15. isValidPassword
16. isValidScreenName
17. isValidUsername