Fix group items by date range function

The problem is that `sorted` function can't compare None-value, but ex.
RentAdjustment model's date fields can be nullable.

By default now, the function converts None date values to min and max
values and can be now sorted correctly.

leasing/models/utils.py

@@ -293,14 +293,22 @@ def split_date_range(date_range, count):
     return result
 
 
-def _get_date_range_from_item(item):
+def _get_date_range_from_item(item, fill_min_max_values=True):
     if isinstance(item, dict):
-        return item["date_range"]
+        start_date, end_date = item["date_range"]
     else:
         if callable(item.date_range):
-            return item.date_range()
+            start_date, end_date = item.date_range()
         else:
-            return item.date_range
+            start_date, end_date = item.date_range
+
+    if fill_min_max_values:
+        if start_date is None:
+            start_date = datetime.date.min
+        if end_date is None:
+            end_date = datetime.date.max
+
+    return start_date, end_date
 
 
 def group_items_in_period_by_date_range(items, min_date, max_date):
@@ -325,7 +333,7 @@ def group_items_in_period_by_date_range(items, min_date, max_date):
     while current_date < max_date:
         current_items = []
         for item in sorted_items:
-            item_range = _get_date_range_from_item(item)
+            item_range = _get_date_range_from_item(item, fill_min_max_values=False)
             if (item_range[0] is None or item_range[0] <= current_date) and (
                 item_range[1] is None or current_date <= item_range[1]
             ):

leasing/tests/models/test_utils.py

@@ -3,6 +3,13 @@
 
 import pytest
 
+from leasing.enums import (
+    DueDatesType,
+    RentAdjustmentAmountType,
+    RentAdjustmentType,
+    RentCycle,
+    RentType,
+)
 from leasing.models.utils import (
     combine_ranges,
     fix_amount_for_overlap,
@@ -725,6 +732,53 @@ def test_group_items_in_period_by_date_range(items, expected):
     )
 
 
+@pytest.mark.django_db
+def test_group_items_in_period_with_nullable_date_model_fields(
+    lease_test_data, rent_factory, decision_factory, rent_adjustment_factory
+):
+
+    lease = lease_test_data["lease"]
+
+    rent = rent_factory(
+        lease=lease,
+        type=RentType.FIXED,
+        cycle=RentCycle.JANUARY_TO_DECEMBER,
+        due_dates_type=DueDatesType.FIXED,
+        due_dates_per_year=1,
+    )
+
+    decision = decision_factory(lease=lease)
+
+    rent_adjustment = rent_adjustment_factory(
+        rent=rent,
+        type=RentAdjustmentType.DISCOUNT,
+        decision=decision,
+        intended_use_id=1,
+        start_date=None,
+        end_date=date(2021, 1, 1),
+        full_amount=12345,
+        amount_type=RentAdjustmentAmountType.AMOUNT_TOTAL,
+    )
+
+    rent_adjustment_2 = rent_adjustment_factory(
+        rent=rent,
+        type=RentAdjustmentType.DISCOUNT,
+        decision=decision,
+        intended_use_id=1,
+        start_date=date(2021, 1, 1),
+        end_date=None,
+        full_amount=12345,
+        amount_type=RentAdjustmentAmountType.AMOUNT_TOTAL,
+    )
+
+    try:
+        group_items_in_period_by_date_range(
+            [rent_adjustment, rent_adjustment_2], date(2015, 9, 1), date(2015, 10, 31)
+        )
+    except Exception as exc:
+        assert False, f"Function raised an exception {exc}"
+
+
 @pytest.mark.parametrize(
     "identifier, expected",
     [