I have this Django model:
from django.contrib.gis.db import models
class Event(models.Model):
address = models.TextField()
point = models.PointField
A quick idea would be to have another boolean field that you mark as true/false when you have an actual point. It would make querying easy because you could add the boolean field to the where clause.
class Event(models.Model):
...
has_point = models.BooleanField(default=False)
point = models.PointField('coordinates', ...)
Event.objects.filter(has_point=True)...#whatever else you need when handling location