Spring AI AdvisedRequest.userText is not populated under some ChatClient Configurations.

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