"Michel Calonne" <Michel.Calonne at etu.univ-savoie.fr> asked:

> And are there other classes behaving the same way?
> So that I can take them in account in my code.
Yes, there are others, too. 
You cannot use the template
  (Smalltalk at: <aClassName>) new
for <aClassName> in 
   { True, False, UndefinedObject, Character, SmallInteger }

When you want to implement a persistence framework you
will have to figure out something special to reload 
  true,  false, nil, the characters and small integers into your
image.

Hope this helps.
Boris