Django set ImageView of User Profile

So i've been working on a project for a while, in which I use the Django default User Instance but with additional attributes, which are stored in a "Profile"-Model. So right now i have an assigned company, and an Profile-Image for the user in the Profile Model.

Now i have a detailview to edit the user's attributes (firstname, username, email, etc.). i used generic.DetailView for this View. But this is only working for the Attributes in the User-Model from Django. How can I also change Attributes in the Profile Model when editing the User?

This is my Edit-View:

class ProfileUpdateView(LoginRequiredMixin, UpdateView):
    model = User
    fields = ['username', 'email', 'first_name', 'last_name']
    template_name = 'inventory/edit_forms/update_profile.html'
    success_url = '/profile'
    login_url = '/accounts/login'
    redirect_field_name = 'redirect_to'

    def form_valid(self, form):
        profile = Profile.objects.get(user=self.request.user)
        profile.img = self.request.POST.get('profile_img')
        profile.save()     

    return super().form_valid(form)


    def get_object(self):
        return User.objects.get(pk = self.request.user.id)

This is my HTML:

<form class="edit_object" action="" method="post" enctype='multipart/form-data' class="form-group">
        <div style="width: 20%; margin-bottom: 1rem;">
          <label>Profile Image</label>
          <input name="profile_img" type="file" accept="image/png, image/gif, image/jpeg">
        </div>
        {% csrf_token %}
        {{form|crispy}}
        <input type="submit" value="Submit" class="btn action_btn">
</form>

As you see i already tried using a external Input field and setting the image like that. But after submitting, the img attribute in the Profile-Model is just set null and I don't know why.

What did I miss?