diff --git a/backend/app/api/runs.py b/backend/app/api/runs.py
index b35cf5d7..78022fbf 100644
--- a/backend/app/api/runs.py
+++ b/backend/app/api/runs.py
@@ -98,9 +98,10 @@ async def consume_astream() -> None:
                     await streamer.send_stream.send(chunk)
                     # hack: function messages aren't generated by chat model
                     # so the callback handler doesn't know about them
-                    message = chunk["messages"][-1]
-                    if isinstance(message, FunctionMessage):
-                        streamer.output[uuid4()] = ChatGeneration(message=message)
+                    if chunk["messages"]:
+                        message = chunk["messages"][-1]
+                        if isinstance(message, FunctionMessage):
+                            streamer.output[uuid4()] = ChatGeneration(message=message)
             except Exception as e:
                 await streamer.send_stream.send(e)
             finally:
diff --git a/backend/packages/agent-executor/agent_executor/permchain.py b/backend/packages/agent-executor/agent_executor/permchain.py
index a472ac32..4ff7c83a 100644
--- a/backend/packages/agent-executor/agent_executor/permchain.py
+++ b/backend/packages/agent-executor/agent_executor/permchain.py
@@ -111,6 +111,10 @@ def get_agent_executor(
     agent_chain = agent | _create_agent_message | Channel.write_to("messages")
 
     def route_last_message(input: dict[str, bool | Sequence[AnyMessage]]) -> Runnable:
+        if not input["messages"]:
+            # no messages, do nothing
+            return RunnablePassthrough()
+
         message: AnyMessage = input["messages"][-1]
         if isinstance(message.additional_kwargs.get("agent"), AgentFinish):
             # finished, do nothing
@@ -137,7 +141,7 @@ def route_last_message(input: dict[str, bool | Sequence[AnyMessage]]) -> Runnabl
         return agent_chain
 
     executor = (
-        Channel.subscribe_to(["messages", ReservedChannels.is_last_step])
+        Channel.subscribe_to(["messages"]).join([ReservedChannels.is_last_step])
         | route_last_message
     )
 
diff --git a/frontend/src/hooks/useStreamState.tsx b/frontend/src/hooks/useStreamState.tsx
index 690b52f4..43a3186a 100644
--- a/frontend/src/hooks/useStreamState.tsx
+++ b/frontend/src/hooks/useStreamState.tsx
@@ -4,7 +4,7 @@ import { Message } from "./useChatList";
 
 export interface StreamState {
   status: "inflight" | "error" | "done";
-  messages: Message[];
+  messages?: Message[];
   run_id?: string;
   merge?: boolean;
 }
@@ -50,13 +50,13 @@ export function useStreamState(): StreamStateProps {
             const { run_id } = JSON.parse(msg.data);
             setCurrent((current) => ({
               status: "inflight",
-              messages: current?.messages ?? [],
+              messages: current?.messages,
               run_id: run_id,
             }));
           } else if (msg.event === "error") {
             setCurrent((current) => ({
               status: "error",
-              messages: current?.messages ?? [],
+              messages: current?.messages,
               run_id: current?.run_id,
             }));
           }
@@ -64,16 +64,18 @@ export function useStreamState(): StreamStateProps {
         onclose() {
           setCurrent((current) => ({
             status: current?.status === "error" ? current.status : "done",
-            messages: current?.messages ?? [],
+            messages: current?.messages,
             run_id: current?.run_id,
+            merge: current?.merge,
           }));
           setController(null);
         },
         onerror(error) {
           setCurrent((current) => ({
             status: "error",
-            messages: current?.messages ?? [],
+            messages: current?.messages,
             run_id: current?.run_id,
+            merge: current?.merge,
           }));
           setController(null);
           throw error;