fix adt 0

adhesions/models.py

@@ -73,10 +73,10 @@ class Adhesion(models.Model):
         return reverse('adhesion-detail', kwargs={'pk': self.pk})
 
     def __str__(self):
-        if self.id:
-            return 'ADT%d (%s)' % (self.id, self.get_adherent_name())
-        else:
+        if self.id is None:
             return '?'
+        else:
+            return 'ADT%d (%s)' % (self.id, self.get_adherent_name())
 
 
 class Corporation(models.Model):