Object class Null safety

The base class for all Dart objects exception null.

Because Object is a root of the non-nullable Dart class hierarchy, every other non-Null Dart class is a subclass of Object.

When you define a class, you should consider overriding toString to return a string describing an instance of that class. You might also need to define hashCode and operator ==, as described in the Implementing map keys section of the library tour.