Verify necessary fields before running model validation tests.

core/models.py

@@ -36,9 +36,10 @@ def validate_unique_period(queryset, model):
     """
     if model.id:
         queryset = queryset.exclude(id=model.id)
+    if model.start and model.end:
         if queryset.filter(start__lte=model.end, end__gte=model.start):
             raise ValidationError(
-            'Another entry already exists within the specified time period.',
+                'Another entry intersects the specified time period.',
                 code='period_intersection')
 
 
@@ -49,7 +50,7 @@ def validate_time(time, field_name):
     :param field_name: the name of the field being checked.
     :return:
     """
-    if time > timezone.localtime():
+    if time and time > timezone.localtime():
         raise ValidationError(
             {field_name: 'Date/time can not be in the future.'},
             code='time_invalid')

core/tests/tests_forms.py

@@ -238,4 +238,4 @@ class FormsTestCase(TestCase):
             page,
             'form',
             None,
-            'Another entry already exists within the specified time period.')
+            'Another entry intersects the specified time period.')