[Zope] problem attach file / Zfile

Hello, I have created a zclass with zfile as basic class. With this class, users could, via a web form, send an attached file if they want. With zope 2.5 (my previous version) if users don't attach a file, there is no problem with zope 2.10, if there is no file attached, I have an error message

[Zope] problem attach file / Zfile - more informations

Hello, I have created a zclass with zfile as basic class. With this class, users could, via a web form, send an attached file if they want. With zope 2.5 (my previous version) if users don't attach a file, there is no problem with zope 2.10, if there is no file attached, I have an error message :