Stock management : Product should have a name

[EveCrystali]

1. Le produit doit porter un nom MissingName (Nom manquant)

_Originally posted by @EveCrystali in #11_

[EveCrystali]

• [x] ModelState.IsValid manage

      [Required(ErrorMessage = "MissingName")]
      public string Name { get; set; }

• [x] Test manuel
• [x] Error Message
• [x] Test auto implementation

[EveCrystali]

fix + auto test ok