'Convert the input JSON value into python structures, raises
django.core.exceptions.ValidationError if the data can\'t be converted.'

def to_python(self, value):

    if (self.blank and (not value)):
        return None
    if isinstance(value, six.string_types):
        try:
            return simplejson.loads(value)
        except Exception as e:
            raise ValidationError(six.text_type(e))
    else:
        return value
