Write your forwards methods here.

def forwards(self, orm):
        "Write your forwards methods here."
        # Note: Don't use "from appname.models import ModelName".
        # Use orm.ModelName to refer to models in this application,
        # and orm['appname.ModelName'] for models in other applications.
        other = orm['assessments.AssessmentCategory'].objects.get(id=7)
        for assessment in orm['assessments.Assessment'].objects.filter(
                assessment_category__isnull=True):
            assessment.assessment_category = other
            assessment.save()