(retriever) follow up markdown review (#1553)

Signed-off-by: Jacob Ioffe <jioffe@nvidia.com>

Author: jioffe502

nemo_retriever/src/nemo_retriever/io/markdown.py

@@ -59,11 +59,11 @@ def to_markdown_by_page(results: object) -> dict[int, str]:
     return rendered
 
 
-def to_markdown(results: object) -> str:
+def to_markdown(results: object) -> str | None:
     """Render a single document result as one markdown document."""
     pages = to_markdown_by_page(results)
     if not pages:
-        return f"# {_DOCUMENT_TITLE}\n\n_No content found._"
+        return None
     return f"# {_DOCUMENT_TITLE}\n\n" + "\n\n".join(pages.values())
 
 
@@ -110,6 +110,9 @@ def _records_from_mapping(results: Mapping[str, Any]) -> list[dict[str, Any]]:
         return [dict(results)]
     raise ValueError("Markdown rendering expects a document row, row list, or saved results payload.")
 
+    # TODO(jioffe): Centralize retriever result-shape detection so helpers and
+    # actor outputs do not rely on duplicated key-based heuristics.
+
 
 def _looks_like_record(record: Mapping[str, Any]) -> bool:
     return any(

nemo_retriever/tests/test_io_markdown.py

@@ -120,8 +120,8 @@ def test_to_markdown_reads_saved_records_wrapper(tmp_path: Path) -> None:
     assert "### Table 1" in markdown
 
 
-def test_to_markdown_empty_results_returns_placeholder() -> None:
-    assert to_markdown([]) == "# Extracted Content\n\n_No content found._"
+def test_to_markdown_empty_results_returns_none() -> None:
+    assert to_markdown([]) is None
 
 
 def test_to_markdown_rejects_multi_document_results() -> None: