Making migrations

picampaign/importer/models.py

 from django.db import models
 from django.utils.translation import ugettext_lazy as _
 
+from picampaign.campaign.models import Campaign
+
 class Importer(models.Model):
     """Importer model. Used to populate campaign with contacts"""
     id = models.AutoField(primary_key=True)
@@ -9,7 +11,7 @@ class Importer(models.Model):
     data_format = models.CharField(max_length=4, choices=[('JSON', 'json'), ('CSV', 'csv')])
     file = models.FileField(upload_to='imports/', blank=True, null=True)
     url = models.URLField(blank=True, null=True)
-    campaign = models.ForeignKey('Campaign', on_delete=models.SET_NULL)
+    campaign = models.ForeignKey(Campaign, on_delete=models.SET_NULL, null=True)
 
     def __str__(self):
         return _(u'%{name}: %{format} %{type} importer' % {'format': self.data_format,