diff --git a/app/item/models.py b/app/item/models.py
index 708adf9..1709e1a 100644
--- a/app/item/models.py
+++ b/app/item/models.py
@@ -7,6 +7,7 @@ import lxml.html
 
 from django.conf import settings
 from django.contrib.auth import get_user_model
+from django.core.exceptions import ValidationError
 from django.db import models
 from django.db.models.functions import ExtractWeek, ExtractYear
 from django.urls import reverse
@@ -48,6 +49,10 @@ class Item(models.Model):
                 self.get_hue()
         super().save(*args, **kwargs)
 
+    def clean(self):
+        if '/m/' not in self.url:
+            raise ValidationError("You can only use mobile urls(/m/)")
+
     def __str__(self):
         return '%s (%s)' % (self.title, self.url)
 
@@ -101,12 +106,14 @@ class Item(models.Model):
         return week, archive
 
     def get_week(self):
-        return int(self.published.strftime('%W'))
+        return int(self.published.strftime('%W')) if self.published else None
 
     def get_year(self):
-        return int(self.published.strftime('%Y'))
+        return int(self.published.strftime('%Y')) if self.published else None
 
     def get_monday(self):
+        if not self.published:
+            return None
         d = '%s-W%s' % (self.get_year(), self.get_week())
         return datetime.strptime(d + '-1', "%Y-W%W-%w").strftime('%Y-%m-%d')