old_contents: # -*- coding: utf-8 -*-
  # Generated by Django 1.11.14 on 2020-02-28 17:30
  from __future__ import unicode_literals
  
  
  from django.db import migrations
  import mimetypes
  
  
  def forward(apps, schema_editor):
      AttachmentModel = apps.get_model('common', 'Attachment')
      for attachment in AttachmentModel.objects.all():
          if mimetypes.guess_type(attachment.attachment_file.name, strict=True)[0].split('/')[0].startswith('image'):
              attachment.is_image = True
              attachment.save()
  
  
  class Migration(migrations.Migration):
  
      dependencies = [
          ('common', '0010_attachment_is_image'),
      ]
  
      operations = [
          migrations.RunPython(forward),
      ]
  
new_contents: # -*- coding: utf-8 -*-
  # Generated by Django 1.11.14 on 2020-02-28 17:30
  from __future__ import unicode_literals
  
  
  from django.db import migrations
  import mimetypes
  
  
  def forward(apps, schema_editor):
      AttachmentModel = apps.get_model('common', 'Attachment')
      for attachment in AttachmentModel.objects.all():
          mt = mimetypes.guess_type(attachment.attachment_file.name, strict=True)[0]
          if mt is not None and mt.split('/')[0].startswith('image'):
              attachment.is_image = True
              attachment.save()
  
  
  class Migration(migrations.Migration):
  
      dependencies = [
          ('common', '0010_attachment_is_image'),
      ]
  
      operations = [
          migrations.RunPython(forward),
      ]
  
subject: Check if mt is None before spliting it