fix json parsing logic and warning message (#833)

* fix json parsing logic and warning message

* amended warning message

---------

Co-authored-by: Alonso Guevara <alonsog@microsoft.com>

Author: ha2trinh

.semversioner/next-release/patch-20240805211407192658.json

@@ -0,0 +1,4 @@
+{
+  "type": "patch",
+  "description": "Change json parsing error in the map step of global search to warning"
+}

graphrag/query/structured_search/global_search/search.py

@@ -192,7 +192,9 @@ async def _map_response_single_batch(
                     # parse search response json
                     processed_response = self.parse_search_response(search_response)
                 except ValueError:
-                    log.exception("Error parsing search response json")
+                    log.warning(
+                        "Warning: Error parsing search response json - skipping this batch"
+                    )
                     processed_response = []
 
             return SearchResult(
@@ -230,15 +232,19 @@ def parse_search_response(self, search_response: str) -> list[dict[str, Any]]:
         """
         search_response, _j = try_parse_json_object(search_response)
         if _j == {}:
-            return [{"answer": "not avaliable", "score": 0}]
+            return [{"answer": "", "score": 0}]
+
+        parsed_elements = json.loads(search_response).get("points")
+        if not parsed_elements or not isinstance(parsed_elements, list):
+            return [{"answer": "", "score": 0}]
 
-        parsed_elements = json.loads(search_response)["points"]
         return [
             {
                 "answer": element["description"],
                 "score": int(element["score"]),
             }
             for element in parsed_elements
+            if "description" in element and "score" in element
         ]
 
     async def _reduce_response(
@@ -277,6 +283,9 @@ async def _reduce_response(
 
             if len(filtered_key_points) == 0 and not self.allow_general_knowledge:
                 # return no data answer if no key points are found
+                log.warning(
+                    "Warning: All map responses have score 0 (i.e., no relevant information found from the dataset), returning a canned 'I do not know' answer. You can try enabling `allow_general_knowledge` to encourage the LLM to incorporate relevant general knowledge, at the risk of increasing hallucinations."
+                )
                 return SearchResult(
                     response=NO_DATA_ANSWER,
                     context_data="",