title: How to use ModelMultipleChoiceFilter in django_filters with JSONfield
body: <p>I'm try filter items use <code>django_filters</code> with <strong>JSONfield</strong> in my model, but I can't do this.</p>
  
  <p>If use <code>CharFields</code> I can get current result, but me need have possibility work on requests.<br>
  When I use <code>ModelMultipleChoiceFilter</code> I get all variations from filter, but filtering does not happen. </p>
  
  <p><code>Models.py</code></p>
  
  <pre class="lang-py prettyprint-override"><code>class Product(models.Model):
      name = models.CharField(max_length=120)
      properties = JSONField(default=dict, blank=True, null=True, db_index=True)
  </code></pre>
  
  <p><code>Filters.py</code></p>
  
  <pre class="lang-py prettyprint-override"><code>from django_filters.rest_framework import FilterSet
  from django_filters import rest_framework as filters
  from products.models import Product
  
  class ProductFilter(FilterSet):
      color = filters.ModelMultipleChoiceFilter(
          queryset=Product.objects.extra(
          select={'color': "properties-&gt;&gt;'color'"}).values_list('properties__color', 
                                                               flat=True).distinct(), 
          field_name='properties', 
          to_field_name='properties',
          lookup_expr='color__contains', 
          )
  
      class Meta:
          model = Product
          fields = {
              'color': 'color__contains',
          }
  </code></pre>
  
  <p><code>This is Item</code></p>
  
  <pre><code>{
      "id": 10,
      "name": "Test_3",
      "properties": {
          "color": "Black",
          "invertor technology": false,
          "service area, m²": 24
      },
  },
  </code></pre>
  
  <p>If I choose in filter color Black,<br>
  I have this error: <strong>Choose the correct option. Black is not among the valid values.</strong></p>