fix: exception on null embedded scalar values

docs/changelog.rst

@@ -24,6 +24,7 @@ Development
 - BugFix - Calling .clear on a ListField wasn't being marked as changed (and flushed to db upon .save()) #2858
 - Improve error message in case a document assigned to a ReferenceField wasn't saved yet #1955
 - BugFix - Take `where()` into account when using `.modify()`, as in MyDocument.objects().where("this[field] >= this[otherfield]").modify(field='new') #2044
+- fix: exception on null embedded scalar values
 
 Changes in 0.29.0
 =================

mongoengine/queryset/base.py

@@ -2036,6 +2036,8 @@ def lookup(obj, name):
             chunks = name.split("__")
             for chunk in chunks:
                 obj = getattr(obj, chunk)
+                if obj is None:
+                    break
             return obj
 
         data = [lookup(doc, n) for n in self._scalar]

tests/queryset/test_queryset.py

@@ -21,6 +21,7 @@
 from mongoengine.queryset import (
     DoesNotExist,
     MultipleObjectsReturned,
+    Q,
     QuerySet,
     QuerySetManager,
     queryset_manager,
@@ -4674,6 +4675,35 @@ class Person(Document):
             ("Gabriel Falcao", 23, "New York"),
         ]
 
+    def test_scalar_embedded_null_parents(self):
+        """Test a multi-scalar query on embedded fields raises an exception when the parent field is null."""
+
+        class EmbeddedModelA(EmbeddedDocument):
+            designator = StringField()
+
+        class Container(Document):
+            source = EmbeddedDocumentField(EmbeddedModelA)
+            target = EmbeddedDocumentField(EmbeddedModelA, null=True)
+
+        # Create one with both values
+        Container(
+            source=EmbeddedModelA(designator="value1"),
+            target=EmbeddedModelA(designator="value2"),
+        ).save()
+
+        # Create one with a null target, but the source value will match the query
+        Container(
+            source=EmbeddedModelA(designator="value1"),
+            target=None,
+        ).save()
+
+        queryset = Container.objects.filter(
+            Q(source__designator="value1") | Q(target__designator="value2")
+        ).values_list("source__designator", "target__designator")
+        # This should not raise an AttributeError on NoneType for the second Container's target__designator
+        values = list(queryset)
+        assert values == [("value1", "value2"), ("value1", None)]
+
     def test_scalar_decimal(self):
         from decimal import Decimal