RDBC-1025: lazily.load(None) now returns Lazy(None) instead of None

`if not ids: return None` returned the bare None value for a None id, so lazy.value raised AttributeError. Now returns Lazy(lambda: None), so lazy.value is None as C# specifies.

Regression test: test_lazy_load_null.py verifies that lazily.load(None) resolves to None without raising AttributeError.

Author: redknightlois

ravendb/documents/session/operations/lazy.py

@@ -191,6 +191,8 @@ def include(self, path: str) -> LazyMultiLoaderWithInclude:
     def load(
         self, ids: Union[List[str], str], object_type: Optional[Type[_T]] = None, on_eval: Callable = None
     ) -> Optional[Lazy[Union[Dict[str, object], object]]]:
+        if ids is None:
+            return Lazy(lambda: None)
         if not ids:
             return None
 

ravendb/tests/session_tests/test_lazy_load_null.py

@@ -0,0 +1,29 @@
+"""
+Lazy load: lazily.load(None) returns a Lazy that resolves to None.
+
+C# reference: SlowTests/Issues/RavenDB_21859.cs
+  Load_And_Lazy_Load_Should_Return_Null_When_Id_Is_Null
+"""
+
+from ravendb.tests.test_base import TestBase
+
+
+class User:
+    def __init__(self, name: str = None):
+        self.name = name
+
+
+class TestRavenDB21859(TestBase):
+    def setUp(self):
+        super().setUp()
+
+    def test_load_null_id_returns_none(self):
+        with self.store.open_session() as session:
+            result = session.load(None, User)
+            self.assertIsNone(result)
+
+    def test_lazily_load_null_id_returns_none(self):
+        with self.store.open_session() as session:
+            lazy = session.advanced.lazily.load(None, User)
+            session.advanced.eagerly.execute_all_pending_lazy_operations()
+            self.assertIsNone(lazy.value)