default value for number of visits set to 0

smash/web/models.py

@@ -115,6 +115,7 @@ class Subject(models.Model):
         verbose_name='ND number'
     )
     visit_count = models.IntegerField(
+	default=0,
         verbose_name='Number of visits'
     )
     mpower_id = models.CharField(max_length=20,