DefaultEquality<E> constructor Null safety

1. Flutter
2. collection
3. DefaultEquality<E>
4. DefaultEquality const constructor

DefaultEquality class

1. Constructors
2. DefaultEquality
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. equals
8. hash
9. isValidKey
10. noSuchMethod
11. toString
12. Operators
13. operator ==