coercing to Unicode: need string or buffer, NoneType found - django

Question

I am making an Ajax request into views as follows:
def all_json_models(request):
data = {}
try:
isp = request.GET['status']
present_isp = Priority.objects.filter(ispname = isp)
isp_count = MultiWAN.objects.all()
# data['latest_no_rules'] = latest_no_rules
#data['present_isp'] = present_isp
data['isp_count'] = isp_count
return HttpResponse(simplejson.dumps(data))
my models.py is like
class MultiWAN(models.Model):
isp_name = models.CharField(max_length=10)
description = models.TextField(null=True)
ip_address = models.IPAddressField(null=True)
subnet = models.IPAddressField(null=True)
gateway = models.IPAddressField(null=True)
nameserver = models.ForeignKey('NameServer')
weight = models.IntegerField(null=False)
interface = models.CharField(max_length=5)
def __unicode__(self):
"""
This function is to return the values we required.
Arguments:
- `self`:
"""
# return u'%s ' % (self.isp_name)
class NameServer(models.Model):
""" A Isp can have more than one nameserver so far we are declearing a seperate table
"""
name = models.IPAddressField(null=False)
class Priority(models.Model):
priority = models.IntegerField(null = True)
ispname = models.ForeignKey('MultiWAN')
rule = models.CharField(max_length=5,null=False)
From = models.IPAddressField(null=True)
To = models.IPAddressField(null=True)
def __unicode__(self):
return u'%s ' % (self.priority)
while making request i am getting the error:
"coercing to Unicode: need string or buffer, NoneType found"
What i am doing wrong here?

Answer 1

It's hard to tell without the full traceback (because it gives information about where in you code the exception is thrown).
The error message "coercing to Unicode: need string or buffer, NoneType found" means that, at some point, django tried to convert something to unicode and expected a string, but received None. This means that either you call a function passing None instead of a string, or one of you methods returns None instead of a string.
In the code you showed us, MultiWAN.__unicode__ seems ill-defined. Maybe the error stems from this ?