AdvisedRequest.userText is not populated under some ChatClient Configurations.

[cpage-pivotal]

Bug description
Under some configurations of ChatClient, AdvisedRequest.userText is not populated, resulting in a message like this:

java.lang.IllegalArgumentException: Content must not be null for SYSTEM or USER messages
	at org.springframework.util.Assert.notNull(Assert.java:181) ~[spring-core-6.2.3.jar:6.2.3]
	at org.springframework.ai.chat.messages.AbstractMessage.<init>(AbstractMessage.java:69) ~[spring-ai-core-1.0.0-M6.jar:1.0.0-M6]
	at org.springframework.ai.chat.messages.UserMessage.<init>(UserMessage.java:62) ~[spring-ai-core-1.0.0-M6.jar:1.0.0-M6]
	at org.springframework.ai.chat.messages.UserMessage.<init>(UserMessage.java:49) ~[spring-ai-core-1.0.0-M6.jar:1.0.0-M6]
	at org.springframework.ai.chat.client.advisor.MessageChatMemoryAdvisor.before(MessageChatMemoryAdvisor.java:97) ~[spring-ai-core-1.0.0-M6.jar:1.0.0-M6]

Environment
Spring ai 1.0.0-M6
Java 21

Steps to reproduce
This simple code reproduces the issue

    @Bean
    ChatMemory chatMemory() {
        return new InMemoryChatMemory();
    }

    @Bean
    CommandLineRunner commandLineRunner(ApplicationContext ctx, ChatClient.Builder chatClientBuilder, ChatMemory chatMemory) {
        return args -> {
            ChatClient chatClient = chatClientBuilder.
                    defaultAdvisors(new MessageChatMemoryAdvisor(chatMemory), new SimpleLoggerAdvisor()).
                    defaultAdvisors(a -> a.param(CHAT_MEMORY_RETRIEVE_SIZE_KEY, 10)).
                    build();

            UserMessage userMessage = new UserMessage("Hello");
            SystemMessage systemMessage = new SystemMessage("You are a poet. Respond in rhymes.");
            Prompt prompt = new Prompt(userMessage,systemMessage);

            String content = chatClient
                    .prompt(prompt)
                    .call()
                    .content();
            System.out.println(content);
        };
    }

Expected behavior
Code should successfully complete chat request.

Minimal Complete Reproducible example
You can fetch and run this repo with the code: https://github.com/cpage-pivotal/advised-request-issue

[sunyuhan1998]

This is because when constructing Prompt, the order of adding Message is very important, which represents the speaking order of the user and the assistant. When ChatClient constructs a request, if you do not explicitly specify userText, it will get the last Message in the Message list to fill in the userText of this request.

In short, in your scenario, you only need to swap the order of userMessage and systemMessage, that is:

Prompt prompt = new Prompt(systemMessage, userMessage);

to solve your problem