title: Image Update threw generic.UpdateView not working
body: <p>I have a Books model class with the following attributes :</p>
  <pre><code>class Books(models.Model):
  
      def get_absolute_url(self):
          return reverse(&quot;books:detail-books&quot;, kwargs={&quot;book_id&quot;: self.pk})
      .......
  
      id = models.AutoField(primary_key=True)
      title = models.CharField(max_length=200, blank=False)
      author = models.CharField(
      verbose_name=&quot;Author (if not you)&quot;, max_length=200, blank=True)
      pub_date = models.DateField(null=True, blank=True)
  
      original_poster = models.ForeignKey(
      PersoUser, on_delete=models.CASCADE)
  
      price = models.DecimalField(
      max_digits=6, decimal_places=2, default=0, validators=[
              MinValueValidator(0)
             ])
  
     cover = models.ImageField(
          default=&quot;cover/default_cover.jpg&quot;, upload_to=&quot;cover&quot;)
  
     def __str__(self):
         return f&quot;{self.title} de {self.author}&quot;
  </code></pre>
  <p>And the user who has posted a book can update it threw a class based view :</p>
  <pre><code>class UpdateBook(LoginRequiredMixin, UserPassesTestMixin, generic.UpdateView):
      model = Books
      form_class = CreateForm
      template_name = &quot;books/update_book.html&quot;
  
      def form_valid(self, form):
          form.instance.original_poster = self.request.user
          return super().form_valid(form)
  
      def test_func(self):
          book = self.get_object()
          if book.original_poster == self.request.user:
              return True
          return False
  </code></pre>
  <p>the form :</p>
  <pre><code>class CreateForm(forms.ModelForm):
  
  class Meta:
  
      model = Books
      exclude = [&quot;original_poster&quot;]
     
  </code></pre>
  <p>When I try to update the price, title or other fields it's working fine but when I try to update the cover image it's not working at all and no error is displayed. It's working when directly updating from the django administration, does anyone have a clue ? I'm quite confused since there is no ptoblem with other fields, thanks in advance</p>