Fix: use "generation" as default response_mode for EmptyIndex (#6534)

* ignore pyrightconfig.json

* use "generation" as default response_mode for EmptyIndex

.gitignore

@@ -143,4 +143,7 @@ modules/
 
 # pipenv
 Pipfile
-Pipfile.lock
+Pipfile.lock
\ No newline at end of file
+
+# pyright
+pyrightconfig.json

llama_index/indices/empty/base.py

@@ -11,6 +11,7 @@ from llama_index.data_structs.data_structs import EmptyIndexStruct
 from llama_index.data_structs.node import Node
 from llama_index.indices.base import BaseIndex
 from llama_index.indices.base_retriever import BaseRetriever
+from llama_index.indices.query.base import BaseQueryEngine
 from llama_index.indices.service_context import ServiceContext
 from llama_index.storage.docstore.types import RefDocInfo
 
@@ -48,6 +49,15 @@ class EmptyIndex(BaseIndex[EmptyIndexStruct]):
 
         return EmptyIndexRetriever(self)
 
+    def as_query_engine(self, **kwargs: Any) -> BaseQueryEngine:
+        if "response_mode" not in kwargs:
+            kwargs["response_mode"] = "generation"
+        else:
+            if kwargs["response_mode"] != "generation":
+                raise ValueError("EmptyIndex only supports response_mode=generation.")
+
+        return super().as_query_engine(**kwargs)
+
     def _build_index_from_nodes(self, nodes: Sequence[Node]) -> EmptyIndexStruct:
         """Build the index from documents.