fix logs

src/backend/base/langflow/api/v1/chat.py

@@ -187,7 +187,8 @@ async def build_vertex(
             logger.exception(f"Error building vertex: {exc}")
             params = format_exception_message(exc)
             valid = False
-            logs = {vertex.outputs[0]["name"]: [Log(message=params, type="error")]}
+            output_label = vertex.outputs[0]["name"] if vertex.outputs else "output"
+            logs = {output_label: [Log(message=params, type="error")]}
             result_data_response = ResultDataResponse(results={})
             artifacts = {}
             # If there's an error building the vertex

src/backend/base/langflow/api/v1/schemas.py

@@ -245,7 +245,7 @@ class VerticesOrderResponse(BaseModel):
 
 class ResultDataResponse(BaseModel):
     results: Optional[Any] = Field(default_factory=dict)
-    logs: dict[str, Log] = Field(default_factory=dict)
+    logs: dict[str, List[Log]] = Field(default_factory=dict)
     message: Optional[Any] = Field(default_factory=dict)
     artifacts: Optional[Any] = Field(default_factory=dict)
     timedelta: Optional[float] = None

src/backend/base/langflow/schema/schema.py

@@ -29,7 +29,7 @@ def build_logs_from_artifacts(artifacts: dict) -> dict:
         elif _type:
             log = Log(message=message, type=_type)
 
-        logs[key] = log
+        logs[key] = [log]
     return logs