The base class for all Dart objects except 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 introduction to dart:core.