Prevent None.cast call

tests/test_processors.py

@@ -1,3 +1,5 @@
+from typing import Type
+
 import pytest
 from lxml.html import fromstring
 from parsel import Selector, SelectorList
@@ -16,12 +18,15 @@
     Image,
     ProductPage,
 )
+from zyte_common_items.components.metadata import Metadata
+from zyte_common_items.items.product import ProductMetadata
 from zyte_common_items.processors import (
     _format_price,
     brand_processor,
     breadcrumbs_processor,
     gtin_processor,
     images_processor,
+    metadata_processor,
     price_processor,
     rating_processor,
 )
@@ -415,3 +420,20 @@ def price(self):
 
     page = PricePage(base_url)  # type: ignore[arg-type]
     assert page.price == expected_value
+
+
+@pytest.mark.parametrize(
+    "input_value,BasePage,expected_value",
+    [
+        (None, ProductPage, None),
+        (Metadata(), ProductPage, ProductMetadata()),
+    ],
+)
+def test_metadata(input_value, BasePage: Type, expected_value):
+    class CustomPage(BasePage):
+        @field(out=[metadata_processor])
+        def metadata(self):
+            return input_value
+
+    page = CustomPage(base_url)  # type: ignore[arg-type]
+    assert page.metadata == expected_value

zyte_common_items/processors.py

@@ -402,9 +402,9 @@ def probability_request_list_processor(
     return [request.cast(ProbabilityRequest) for request in request_list]
 
 
-def metadata_processor(metadata: BaseMetadata, page):
+def metadata_processor(metadata: Optional[BaseMetadata], page):
     """Processor for a metadata field that ensures that the output metadata
     object uses the metadata class declared by *page*."""
-    if page.metadata_cls is None:
+    if metadata is None or page.metadata_cls is None:
         return None
     return metadata.cast(page.metadata_cls)