is not JSON serializable

[olivx]

I'm still using , Django 1.8 and python 2.7 ...

when i try to save my model , i receive the error...
<django.utils.functional.proxy object at 0x7f5ffe8cd590> is not JSON serializable

my method:
if not CustomStatusStep.objects.filter(company=obj, title=(u'Aberta')):
CustomStatusStep.objects.create(
company=obj,
title=(u'Aberta'),
creator=request.user,
standard=True ...
)

and the error, i believes is in this part:
if created:
changes = model_instance_diff(None, instance)
log_entry = LogEntry.objects.log_create(
instance,
action=LogEntry.Action.CREATE,
changes=json.dumps(changes), ...
)

i believes , the error ocorre when i pass this parameter
title=_(u'Aberta') ....

there is some hack for this ?
so, how i can use ugettext_lazy whith django-udity-log ?