title: null=True,blank=True but still error may not be null is raised everytime during post
body: <p>my model:</p>
  
  <pre><code>    Assets(modes.Model):
        assset_code=models.CharField(max_length=12,null=True,blank=True)
  </code></pre>
  
  <p>In my serializers.py:</p>
  
  <pre><code> asset_code=serializers.CharField(max_length=12,allow_blank=True,required=False)
  </code></pre>
  
  <p>When I post data, it still says this field may not be null. It lets me pass only if I put data.</p>
  
  <p>While I am at it, whats the correct way to make JSONField() optional in serializers too?</p>