community[patch]: Fix NotionDBLoader 400 Error by conditionally adding filter parameter (#19075)

- **Description:** This change fixes a bug where attempts to load data
from Notion using the NotionDBLoader resulted in a 400 Bad Request
error. The issue was traced to the unconditional addition of an empty
'filter' object in the request payload, which Notion's API does not
accept. The modification ensures that the 'filter' object is only
included in the payload when it is explicitly provided and not empty,
thus preventing the 400 error from occurring.
- **Issue:** Fixes
[#18009](https://github.com/langchain-ai/langchain/issues/18009)
- **Dependencies:** None
- **Twitter handle:** @gunnzolder

Co-authored-by: Anton Parkhomenko <anton@merge.rocks>

libs/community/langchain_community/document_loaders/notiondb.py

@@ -207,11 +207,14 @@ class NotionDBLoader(BaseLoader):
         *,
         filter_object: Optional[Dict[str, Any]] = None,
     ) -> Any:
+        json_payload = query_dict.copy()
+        if filter_object:
+            json_payload["filter"] = filter_object
         res = requests.request(
             method,
             url,
             headers=self.headers,
-            json={**query_dict, "filter": filter_object or {}},
+            json=json_payload,
             timeout=self.request_timeout_sec,
         )
         res.raise_for_status()