old_contents: from __future__ import unicode_literals
  
  from django_evolution.mutations import AddField
  from django.db import models
  
  
  MUTATIONS = [
      AddField('FileAttachment', 'uuid', models.CharField, max_length=255,
               initial=None, null=True),
  ]
  
new_contents: from __future__ import unicode_literals
  
  from django_evolution.mutations import AddField
  from django.db import models
  
  
  MUTATIONS = [
      AddField('FileAttachment', 'uuid', models.CharField, max_length=255,
               initial=''),
  ]
  
subject: Fix the FileAttachment.uuid evolution to match the model field.