pilkit error

gistfile1.pytb

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ERROR: test_hero_images_not_regenerated_when_crop_doesnt_change (fileupload.tests.test_models.FileuploadImageModelTests)
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Traceback (most recent call last):
  File "/Users/jacob/Documents/Projects/gizmag/fileupload/tests/test_models.py", line 216, in test_hero_images_not_regenerated_when_crop_doesnt_change
    self.image.save()
  File "/Users/jacob/Documents/Projects/gizmag/fileupload/models.py", line 166, in save
    super(Image, self).save(*args, **kwargs)
  File "/Users/jacob/Documents/Projects/gizmag/fileupload/models.py", line 51, in save
    super(BaseMedia, self).save(*args, **kwargs)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/django/db/models/base.py", line 546, in save
    force_update=force_update, update_fields=update_fields)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/django/db/models/base.py", line 664, in save_base
    update_fields=update_fields, raw=raw, using=using)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/django/dispatch/dispatcher.py", line 170, in send
    response = receiver(signal=self, sender=sender, **named)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/imagekit/specs/sourcegroups.py", line 33, in receiver
    fn(self, sender=sender, **kwargs)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/imagekit/specs/sourcegroups.py", line 97, in post_save_receiver
    attname)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/imagekit/specs/sourcegroups.py", line 112, in dispatch_signal
    signal.send(sender=source_group, source=file)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/django/dispatch/dispatcher.py", line 170, in send
    response = receiver(signal=self, sender=sender, **named)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/imagekit/registry.py", line 113, in source_group_receiver
    call_strategy_method(file, callback_name)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/imagekit/utils.py", line 132, in call_strategy_method
    fn(file)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/imagekit/cachefiles/strategies.py", line 27, in on_source_saved
    file.generate()
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/imagekit/cachefiles/__init__.py", line 92, in generate
    self.cachefile_backend.generate(self, force)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/imagekit/cachefiles/backends.py", line 108, in generate
    self.generate_now(file, force=force)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/imagekit/cachefiles/backends.py", line 96, in generate_now
    file._generate()
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/imagekit/cachefiles/__init__.py", line 96, in _generate
    content = generate(self.generator)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/imagekit/utils.py", line 115, in generate
    content = generator.generate()
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/imagekit/specs/__init__.py", line 158, in generate
    options=self.options)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/pilkit/utils.py", line 301, in process_image
    return img_to_fobj(img, format, autoconvert, **options)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/pilkit/utils.py", line 16, in img_to_fobj
    return save_image(img, StringIO(), format, options, autoconvert)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/pilkit/utils.py", line 166, in save_image
    img.save(outfile, format, **options)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/PIL/Image.py", line 1452, in save
    save_handler(self, fp, filename)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/PIL/JpegImagePlugin.py", line 571, in _save
    ImageFile._save(im, fp, [("jpeg", (0,0)+im.size, 0, rawmode)], bufsize)
  File "/Users/jacob/.virtualenvs/gizmag/lib/python2.7/site-packages/PIL/ImageFile.py", line 467, in _save
    fp.write(d)
TypeError: string argument expected, got 'str'