LLMRanker returns documents unranked on None query instead of crashing

haystack/components/rankers/llm_ranker.py

@@ -253,7 +253,7 @@ def run(self, query: str, documents: list[Document], top_k: int | None = None) -
         deduplicated_documents = _deduplicate_documents(documents)
         fallback_documents = deduplicated_documents
 
-        if not query.strip():
+        if not isinstance(query, str) or not query.strip():
             logger.warning("Empty query provided to LLMRanker. Returning documents without reranking.")
             return {"documents": fallback_documents}
 
@@ -320,7 +320,7 @@ async def run_async(
         deduplicated_documents = _deduplicate_documents(documents)
         fallback_documents = deduplicated_documents
 
-        if not query.strip():
+        if not isinstance(query, str) or not query.strip():
             logger.warning("Empty query provided to LLMRanker. Returning documents without reranking.")
             return {"documents": fallback_documents}
 

releasenotes/notes/llm-ranker-none-query-fallback-4f2a1c9d8b3e7f5a.yaml

@@ -0,0 +1,6 @@
+fixes:
+  - |
+    ``LLMRanker`` no longer crashes with ``AttributeError`` when ``query`` is
+    ``None`` (or another non-string) coming from an upstream pipeline
+    component. Both ``run`` and ``run_async`` now return the documents
+    unranked, matching the existing empty-query fallback.

test/components/rankers/test_llm_ranker.py

@@ -122,6 +122,15 @@ def test_run_whitespace_query_returns_fallback(mock_chat_generator):
     mock_chat_generator.run.assert_not_called()
 
 
+@pytest.mark.parametrize("bad_query", [None, 123])
+def test_run_non_string_query_returns_fallback(mock_chat_generator, bad_query):
+    documents = [Document(id="1", content="first"), Document(id="2", content="second")]
+    ranker = LLMRanker(chat_generator=mock_chat_generator)
+
+    assert ranker.run(query=bad_query, documents=documents) == {"documents": documents}
+    mock_chat_generator.run.assert_not_called()
+
+
 def test_run_successful_ranking():
     documents = [
         Document(id="1", content="first"),
@@ -417,6 +426,16 @@ async def test_run_async_generator_exception_raises(self):
         with pytest.raises(RuntimeError, match="generator failed"):
             await ranker.run_async(query="test query", documents=documents)
 
+    @pytest.mark.asyncio
+    async def test_run_async_none_query_returns_fallback(self):
+        documents = [Document(id="1", content="first"), Document(id="2", content="second")]
+        mock_chat_generator = Mock(spec=OpenAIChatGenerator)
+        mock_chat_generator.run_async = AsyncMock()
+        ranker = LLMRanker(chat_generator=mock_chat_generator)
+
+        assert await ranker.run_async(query=None, documents=documents) == {"documents": documents}  # type: ignore[arg-type]
+        mock_chat_generator.run_async.assert_not_called()
+
     @pytest.mark.integration
     @pytest.mark.skipif(
         not os.environ.get("OPENAI_API_KEY", None),