title: Django Admin filter then exclude not working in my project
body: <p>When i am filtering, i am getting all the products name , that i am not expecting also those products are not assigned to any country just list of name products.</p>
  <p>i made this query to exclude but not working.</p>
  <p>admin.py</p>
  <pre><code>    def formfield_for_manytomany(self, db_field, request, product_name=None, product_name__isnull= True, **kwargs):
      if db_field.name == &quot;product_name&quot; :
          kwargs[&quot;queryset&quot;] = models.ProductName.objects.filter(product_name == request._user_country).exclude(product_name__exists == None)
      return super().formfield_for_foreignkey(db_field, request, **kwargs)
  </code></pre>
  <p>model.py</p>
  <pre><code>class Product(models.Model):
  name = models.ManyToManyField(
      ProductName, verbose_name=_(&quot;Products Name&quot;)
  country = models.ForeignKey(Country, on_delete=models.CASCADE, verbose_name=_(&quot;Country&quot;))
  </code></pre>