Why is Object not considered a superclass for null?

[Igor Molchanov]

According to the documentation, I can get the following information:

Some other types also have special roles in the Dart language:

• Object: The superclass of all Dart classes except Null.

However, when creating the dump of kernel binary file I can find the following lines:

@/* from org-dartlang-sdk:///sdk/lib/_internal/vm_shared/lib/null_patch.dart */ #C55
  @/* from org-dartlang-sdk:///sdk/lib/_internal/vm_shared/lib/null_patch.dart */ #C433
  @/* from org-dartlang-sdk:///sdk/lib/_internal/vm_shared/lib/null_patch.dart */ #C3
  @#C3
  final class Null extends core::Object { // from org-dartlang-sdk:///sdk/lib/core/null.dart
    static const field core::int _HASH_CODE = #C2837 /* from org-dartlang-sdk:///sdk/lib/_internal/vm_shared/lib/null_patch.dart */;
    get /* from org-dartlang-sdk:///sdk/lib/_internal/vm_shared/lib/null_patch.dart */ _identityHashCode() → core::int
      return #C2837;
    static factory _uninstantiable() → Null {
      throw new core::UnsupportedError::•("class Null cannot be instantiated");
    }
    @#C55
    get /* from org-dartlang-sdk:///sdk/lib/_internal/vm_shared/lib/null_patch.dart */ hashCode() → core::int
      return #C2837;
    method toString() → core::String
      return "null";
  }

They show that null is inherited from the object, and also implements toString and hashCode in patches.
I can find the relevant information in the language specification (chapter 17.4):

The Null class extends the Object class
and declares no methods except those also declared by Object. In particular, the Null class does not override the ‘==’ operator inherited from the Object class.

Why is it considered that object is not a superclass for null?
If not, is the superclass formulation correct and should we explain this language behavior in more detail in the documentation?

[Slava Egorov]

The way Null is defined in Kernel is an implementation detail. What specification says is that null is Object evaluates to false.

[Lasse R.H. Nielsen]

That language specification does not include the Null Safety feature, and is no longer correct. Null is not a subclass or subtype of Object.
Implementations may cheat, but as long as you can't tell, it's OK.

As for why Null is not a subclass of Object, it's because then there is a supertype for all non-null values.
Without that, you could do, fx, T? valueOf<T extends Object>(T value, bool useValue) => useValue ? value : null; and know that the value will not itself be null.

[Igor Molchanov]

Thanks for the answers! It's much clearer to me now how it works.