[BUG] IllegalException"text cannot be null" when using Qianfan Model

[yao-wenbin]

Describe the bug

when I using qianfan model, If api reach the limited, Model's generate() method will throw Illegal Exception instead of clear err response.

Log and Stack trace

Exception in thread "main" java.lang.IllegalArgumentException: text cannot be null
	at dev.langchain4j.internal.Exceptions.illegalArgument(Exceptions.java:19)
	at dev.langchain4j.internal.ValidationUtils.ensureNotNull(ValidationUtils.java:50)
	at dev.langchain4j.internal.ValidationUtils.ensureNotNull(ValidationUtils.java:37)
	at dev.langchain4j.data.message.AiMessage.<init>(AiMessage.java:30)
	at dev.langchain4j.data.message.AiMessage.from(AiMessage.java:116)
	at dev.langchain4j.data.message.AiMessage.aiMessage(AiMessage.java:146)
	at dev.langchain4j.model.qianfan.InternalQianfanHelper.aiMessageFrom(InternalQianfanHelper.java:162)
	at dev.langchain4j.model.qianfan.QianfanChatModel.generate(QianfanChatModel.java:131)
	at dev.langchain4j.model.qianfan.QianfanChatModel.generate(QianfanChatModel.java:95)
	at com.github.yaowenbin.functioncalling.GetWeatherExample.main(GetWeatherExample.java:32)

To Reproduce

Using qianfan model and provide a reached limit api key and then call model's generate().

    var model = QianfanChatModel.builder()
            .modelName("ERNIE-Bot")
            .apiKey(System.getenv("QIANFAN_API_KEY"))
            .secretKey(System.getenv("QIANFAN_SECRET_KEY"))
            .build();
        UserMessage userMessage = UserMessage.from("What is the square root of 475695037565?");
        Response<AiMessage> response = model.generate(Collections.singletonList(userMessage));

Expected behavior

If API reached limit, generate() method should throw a more clear exception instead of IllegalException: text cannot be null.

Please complete the following information:

• LangChain4j version: 3.0.0
• LLM(s) used: Qianfan
• Java version: 17
• Spring Boot version (if applicable):

Additional context

[dosubot]

Hey there, @yao-wenbin! 🎉 I'm Dosu, a bot here to help you solve bugs, answer questions, and even guide you on becoming a contributor. While we're waiting for a human maintainer to chime in, I'm here to assist you. Just wanted to let you know that I'm taking a look at your issue with the Qianfan Model and will provide you with a full answer shortly. Stay tuned!

[yao-wenbin]

It's a debug in QianfanModel's generate() method

[yao-wenbin]

@langchain4j hi, could you assign me to this issue? I'll work on it today

[yao-wenbin]

@langchain4j hello, I already create a pr for this issue, It my first time to contribute code to this repository.
Could you give me a code review or something other advices?I will appreciate that.
Thank you! has a nice day