Catch invalid object ID in form initial setup

Fixes #735

core/forms.py

@@ -9,6 +9,7 @@ from taggit.forms import TagField
 
 from babybuddy.widgets import DateInput, DateTimeInput, TimeInput
 from core import models
+from core.models import Timer
 from core.widgets import TagsEditor, ChildRadioSelect
 
 
@@ -43,10 +44,13 @@ def set_initial_values(kwargs, form_type):
     # Set start and end time based on Timer from `timer` kwarg.
     timer_id = kwargs.get("timer", None)
     if timer_id:
+        try:
             timer = models.Timer.objects.get(id=timer_id)
             kwargs["initial"].update(
                 {"timer": timer, "start": timer.start, "end": timezone.now()}
             )
+        except Timer.DoesNotExist:
+            pass
 
     # Set type and method values for Feeding instance based on last feed.
     if form_type == FeedingForm and "child" in kwargs["initial"]:

core/tests/tests_forms.py

@@ -124,10 +124,13 @@ class InitialValuesTestCase(FormsTestCaseBase):
         self.assertEqual(page.context["form"].initial["type"], f_three.type)
         self.assertEqual(page.context["form"].initial["method"], f_three.method)
 
-    def test_timer_form_field_set(self):
-        self.timer.stop()
+    def test_start_end_set_from_timer(self):
+        page = self.c.get("/sleep/add/?timer={}".format(self.timer.id))
+        self.assertTrue("start" in page.context["form"].initial)
+        self.assertTrue("end" in page.context["form"].initial)
 
-        page = self.c.get("/sleep/add/")
+    def test_start_end_not_set_from_invalid_timer(self):
+        page = self.c.get("/sleep/add/?timer={}".format(42))
         self.assertTrue("start" not in page.context["form"].initial)
         self.assertTrue("end" not in page.context["form"].initial)