title: Django GraphQL returns null
body: <p>I have a Django GraphQL app (<em>graphene_django</em>) running with djongo (<em>mongoDB</em>).</p>
  
  <p>When I try to list all twitter queries (<em>with GraphiQL</em>), it returns null data :</p>
  
  <p>My query :</p>
  
  <pre><code>query {
    allTwitterQueries {
      id,
      keyword
    }
  }
  </code></pre>
  
  <p>Returns :</p>
  
  <pre><code>{
    "data": {
      "allTwitterQueries": null
    }
  }
  </code></pre>
  
  <p>Here are my Django files :</p>
  
  <p>untitled/schema.py</p>
  
  <pre class="lang-py prettyprint-override"><code>import untitled.api.schema
  import graphene
  
  from graphene_django.debug import DjangoDebug
  
  
  class Query(
      untitled.api.schema.Query,
      graphene.ObjectType,
  ):
      debug = graphene.Field(DjangoDebug, name="_debug")
  
  
  schema = graphene.Schema(query=Query)
  </code></pre>
  
  <p>untitled/api/models.py</p>
  
  <pre class="lang-py prettyprint-override"><code>from django.db import models
  from django.contrib.auth.models import User
  
  
  class TwitterQuery(models.Model):
      user_key = models.ForeignKey(User, related_name="created_by", on_delete=models.CASCADE, default=0)
      keyword = models.TextField(default="null")
      active = models.BooleanField(null=True)
      created_at = models.BigIntegerField(default=0)
      updated_at = models.BigIntegerField(default=0)
      count = models.IntegerField(default=0)
  
      def __str__(self):
          return self.keyword
  </code></pre>
  
  <p>untitled/api/schema.py</p>
  
  <pre class="lang-py prettyprint-override"><code>import graphene
  from graphene_django.types import DjangoObjectType
  
  from untitled.api.models import TwitterQuery
  
  
  class TwitterQueryType(DjangoObjectType):
      class Meta:
          model = TwitterQuery
  
  
  class Query(object):
      twitter_query = graphene.Field(TwitterQueryType, id=graphene.Int(), keyword=graphene.String(), active=graphene.Boolean())
      all_twitter_queries = graphene.List(TwitterQueryType)
  
      def fetch_twitter_queries(self, context):
          return TwitterQuery.objects.all()
  
      def fetch_twitter_query(self, context, user_id=None, active=None):
          if user_id is not None:
              return TwitterQuery.objects.get(user_id=user_id)
          if active is not None:
              return TwitterQuery.objects.get(active=active)
  
          return None
  </code></pre>
  
  <p>I have one item in my mongoDB instance : </p>
  
  <pre><code>{"_id":{"$oid":"5df20401d4e39b1e89223b15"},
  "id":{"$numberInt":"1"},
  "user_key_id":{"$numberInt":"1"},
  "keyword":"greve",
  "active":true,
  "created_at":{"$numberLong":"1575846000000"},
  "updated_at":{"$numberLong":"1575846000000"},
  "count":{"$numberInt":"0"}}
  </code></pre>