fix: Inject kg context even if kg query result is empty (#198)

* fix some bugs in reflexion agent

* fix an vectorstore issue

* introduce use_reflexion to kg RagAgent

* prompt LLM not to generate cypher marker

* fix test error

* change vectorstore collection names to apply previous fix of collection field max length issue

* phrasing, formatting, parameter explanations

* fix type hinting

* prompt LLM even if kg query result is empty

---------

Co-authored-by: fengsh <shaohong.feng.78@gmail.com>
Co-authored-by: slobentanzer <sebastian.lobentanzer@gmail.com>

biochatter/database_agent.py

@@ -115,6 +115,21 @@ def get_query_results(self, query: str, k: int = 3) -> list[Document]:
         # than k
         if results is None or len(results) == 0 or results[0] is None:
             return []
+        if len(results[0]) == 0:
+            return [
+                Document(
+                    page_content = (
+                        "I didn't find any result in knowledge graph, "
+                        f"but here is the query I used: {cypher_query}. "
+                        "You can ask user to refine the question, "
+                        "but don't make up anything."
+                    ),
+                    metadata={
+                        "cypher_query": cypher_query,
+                    },
+                )
+            ]
+
         for result in results[0]:
             documents.append(
                 Document(