[#243] fix nested expand values

src/openklant/components/utils/expansion.py

@@ -66,20 +66,19 @@ def display_children(self) -> dict:
         """
         results = {}
         for child in self._children:
-            # TODO: rewrite display function?
-            child_result = child.display() if child.value else None
+            child_result = child.display()
 
             if child.many:
                 child_results = results.setdefault(child.label, [])
 
-                if child_result:
+                if child_result is not None:
                     child_results.append(child_result)
             else:
                 results[child.label] = child_result
         return results
 
-    def display(self) -> dict:
-        data = self.value.copy()
+    def display(self) -> Optional[dict]:
+        data = self.value.copy() if self.value is not None else None
         if self._children:
             data[EXPAND_KEY] = self.display_children()
         return data
@@ -254,6 +253,8 @@ def _field_inclusions(
             True if hasattr(field, "child_relation") else getattr(field, "many", False)
         )
 
+        obj: Optional[models.Model] = None
+
         for obj in self._some_related_field_inclusions(
             new_path, field, instance, inclusion_serializer
         ):
@@ -269,7 +270,7 @@ def _field_inclusions(
                 yield entry
         else:
             if new_path in self.allowed_paths:
-                yield None, inclusion_serializer, instance, new_path, many
+                yield obj, inclusion_serializer, instance, new_path, many
 
     def _some_related_field_inclusions(
         self,