From f55ff3a822ea6d32bb7a671a3487c463fb25af19 Mon Sep 17 00:00:00 2001 From: Kian Jones <11655409+kianjones9@users.noreply.github.com> Date: Thu, 12 Feb 2026 17:02:45 -0800 Subject: [PATCH] fix(core): descriptive error for empty message_ids instead of IndexError (#9464) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit fix(core): replace IndexError with descriptive error for empty message_ids Agent with no in-context messages (empty/None message_ids) would crash with a cryptic IndexError on message_ids[0]. Now raises a clear LettaError explaining the system message was not initialized. Datadog: https://us5.datadoghq.com/error-tracking/issue/6c061c28-0830-11f1-b060-da7ad0900000 🐾 Generated with [Letta Code](https://letta.com) Co-authored-by: Letta --- letta/agents/helpers.py | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/letta/agents/helpers.py b/letta/agents/helpers.py index 41328da5..b99c8d44 100644 --- a/letta/agents/helpers.py +++ b/letta/agents/helpers.py @@ -4,7 +4,7 @@ import xml.etree.ElementTree as ET from typing import Any, Dict, List, Optional, Tuple from uuid import UUID, uuid4 -from letta.errors import PendingApprovalError +from letta.errors import LettaError, PendingApprovalError from letta.helpers import ToolRulesSolver from letta.helpers.datetime_helpers import get_utc_time from letta.log import get_logger @@ -233,6 +233,11 @@ async def _prepare_in_context_messages_no_persist_async( current_in_context_messages = [system_message] else: # Default mode: load messages from agent_state.message_ids + if not agent_state.message_ids: + raise LettaError( + message=f"Agent {agent_state.id} has no in-context messages. " + "This typically means the agent's system message was not initialized correctly.", + ) if agent_state.message_buffer_autoclear: # If autoclear is enabled, only include the most recent system message (usually at index 0) current_in_context_messages = [