Update the default on the category to be the empty json dict

opentech/public/projects/migrations/0004_projectpage_categories.py

 # -*- coding: utf-8 -*-
-# Generated by Django 1.11.8 on 2018-01-17 22:22
+# Generated by Django 1.11.8 on 2018-01-18 10:03
 from __future__ import unicode_literals
 
 from django.db import migrations, models
@@ -16,6 +16,5 @@ class Migration(migrations.Migration):
             model_name='projectpage',
             name='categories',
             field=models.TextField(default='{}'),
-            preserve_default=False,
         ),
     ]

opentech/public/projects/models.py

@@ -109,7 +109,7 @@ class ProjectPage(FundingMixin, BasePage):
     status = models.CharField(choices=STATUSES, max_length=25, default=STATUSES[0][0])
     body = StreamField(StoryBlock())
 
-    categories = models.TextField()
+    categories = models.TextField(default="{}")
 
     search_fields = BasePage.search_fields + [
         index.SearchField('introduction'),
@@ -131,6 +131,7 @@ class ProjectPage(FundingMixin, BasePage):
         options = [int(id) for options in categories.values() for id in options]
         return Option.objects.select_related().filter(id__in=options).order_by('category')
 
+
 class ProjectIndexPage(BasePage):
     subpage_types = ['ProjectPage']
     parent_page_types = ['home.Homepage']