alibaba/spring-ai-alibaba · warning

No messages found in state when routing from model to tools

Error message

No messages found in state when routing from model to tools

What it means

ReactAgent's model-to-tools routing edge reads the 'messages' key from graph state to inspect the last message's tool calls. If the state has no messages at routing time, it logs this warning and routes to the END destination instead of the tools node, ending the run.

Solutions

1. Ensure the model node stores its AssistantMessage under the standard 'messages' state key
2. Do not set an outputKey on the ReactAgent that diverts messages away from 'messages' when tool routing is used
3. Verify checkpoints/state include 'messages' when resuming
4. Add a guard in custom graphs to initialize 'messages' before routing

Example fix

// before
node writes: state.set("model_output", assistantMessage); // 'messages' stays empty
// after
node appends: new AppendableValue<>("messages", assistantMessage); // routing sees the message

List<Message> messages = (List<Message>) state.value("messages").orElse(List.of());
if (messages.isEmpty()) { throw new IllegalStateException("'messages' state key must be populated before model-to-tools routing"); }

static boolean hasMessages(Map<String,Object> state) { Object m = state.get("messages"); return m instanceof List<?> l && !l.isEmpty(); }

When it happens

Trigger: makeModelToTools routing function executes while state.value("messages") is empty — the model node produced no messages into state before the conditional edge was evaluated.

Common situations: Custom state graph replacing the default messages key; model node writing output to a different key (e.g. via outputKey) so 'messages' stays empty; state reducer misconfigured; resuming from a checkpoint that lacks messages.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

• ReactAgent requires model configuration in handle
• Unsupported DTO type:
• Unsupported message type
• Unsupported message type:

AI-assisted analysis of alibaba/spring-ai-alibaba@f82da0b50f (2026-09-09). Data as JSON: /api/errors/cc6f78288611c699. Report an issue: GitHub.

Appendix: source

Thrown at spring-ai-alibaba-agent-framework/src/main/java/com/alibaba/cloud/ai/graph/agent/ReactAgent.java:788

					jumpTo = (JumpTo) jumpToValue;
				} else if (jumpToValue instanceof String) {
					jumpTo = JumpTo.fromStringOrNull((String) jumpToValue);
				}
				
				// If a valid jump_to instruction exists, execute it immediately
				if (jumpTo != null) {
					return switch (jumpTo) {
						case model -> modelDestination;
						case end -> endDestination;
						case tool -> AGENT_TOOL_NAME;
					};
				}
			}
			
			// Priority 2: Check message content for tool calls
			List<Message> messages = (List<Message>) state.value("messages").orElse(List.of());
			if (messages.isEmpty()) {
				logger.warn("No messages found in state when routing from model to tools");
				return endDestination;
			}
			Message lastMessage = messages.get(messages.size() - 1);

			// 1. Check the last message type
			if (lastMessage instanceof AssistantMessage assistantMessage) {
				// 2. If last message is AssistantMessage
				if (assistantMessage.hasToolCalls()) {
					return AGENT_TOOL_NAME;
				} else {
					return endDestination;
				}
			} else if (lastMessage instanceof ToolResponseMessage) {
				// 3. If last message is ToolResponseMessage
				if (messages.size() < 2) {
					// Should not happen in a valid ReAct loop, but as a safeguard.
					throw new RuntimeException("Less than 2 messages in state when last message is ToolResponseMessage");
				}

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