Check.in_grace_period() should not blow up if last_ping is None

hc/api/models.py

@@ -91,6 +91,9 @@ class Check(models.Model):
         return "down"
 
     def in_grace_period(self):
+        if not self.last_ping:
+            return False
+
         up_ends = self.last_ping + self.timeout
         grace_ends = up_ends + self.grace
         return up_ends < timezone.now() < grace_ends

hc/api/tests/test_check_model.py

@@ -13,3 +13,7 @@ class CheckModelTestCase(TestCase):
 
         check.tags = " "
         self.assertEquals(check.tags_list(), [])
+
+    def test_in_grace_period_handles_new_check(self):
+        check = Check()
+        self.assertFalse(check.in_grace_period())