Hotfix: Qdrant content retrieval (revert: #1088) (#1093)

The #1088 introduced a bug in Qdrant integration. That PR reverts those
changes and provides class attributes to ensure consistent payload keys.
In addition to that, an exception will be thrown if any of texts is None
(that could have been an issue reported in #1087)

langchain/vectorstores/qdrant.py

@@ -25,6 +25,9 @@ class Qdrant(VectorStore):
             qdrant = Qdrant(client, collection_name, embedding_function)
     """
 
+    CONTENT_KEY = "page_content"
+    METADATA_KEY = "metadata"
+
     def __init__(self, client: Any, collection_name: str, embedding_function: Callable):
         """Initialize with necessary components."""
         try:
@@ -213,17 +216,25 @@ class Qdrant(VectorStore):
     def _build_payloads(
         cls, texts: Iterable[str], metadatas: Optional[List[dict]]
     ) -> List[dict]:
-        return [
-            {
-                "page_content": text,
-                "metadata": metadatas[i] if metadatas is not None else None,
-            }
-            for i, text in enumerate(texts)
-        ]
+        payloads = []
+        for i, text in enumerate(texts):
+            if text is None:
+                raise ValueError(
+                    "At least one of the texts is None. Please remove it before "
+                    "calling .from_texts or .add_texts on Qdrant instance."
+                )
+            payloads.append(
+                {
+                    cls.CONTENT_KEY: text,
+                    cls.METADATA_KEY: metadatas[i] if metadatas is not None else None,
+                }
+            )
+
+        return payloads
 
     @classmethod
     def _document_from_scored_point(cls, scored_point: Any) -> Document:
         return Document(
-            page_content=scored_point.payload.get("content"),
-            metadata=scored_point.payload.get("metadata") or {},
+            page_content=scored_point.payload.get(cls.CONTENT_KEY),
+            metadata=scored_point.payload.get(cls.METADATA_KEY) or {},
         )