[BUG] Streaming AI Service: a NullPointerException when using non-OpenAI APIs

[hehr]

Describe the bug

java.lang.NullPointerException

Log and Stack trace

at dev.langchain4j.model.output.TokenUsage.add(TokenUsage.java:88) ~[langchain4j-core-0.29.1.jar:na]
at dev.langchain4j.service.AiServiceStreamingResponseHandler.onComplete(AiServiceStreamingResponseHandler.java:92) ~[langchain4j-0.29.1.jar:na]
at dev.langchain4j.model.openai.OpenAiStreamingChatModel.lambda$generate$1(OpenAiStreamingChatModel.java:166) ~[langchain4j-open-ai-0.29.1.jar:na]
at dev.ai4j.openai4j.StreamingRequestExecutor$2.onEvent(StreamingRequestExecutor.java:170) ~[openai4j-0.17.0.jar:na]
at okhttp3.internal.sse.RealEventSource.onEvent(RealEventSource.kt:101) [okhttp-sse-4.9.3.jar:na]
at okhttp3.internal.sse.ServerSentEventReader.completeEvent(ServerSentEventReader.kt:108) ~[okhttp-sse-4.9.3.jar:na]
at okhttp3.internal.sse.ServerSentEventReader.processNextEvent(ServerSentEventReader.kt:52) ~[okhttp-sse-4.9.3.jar:na]
at okhttp3.internal.sse.RealEventSource.processResponse(RealEventSource.kt:75) [okhttp-sse-4.9.3.jar:na]
at okhttp3.internal.sse.RealEventSource.onResponse(RealEventSource.kt:46) [okhttp-sse-4.9.3.jar:na]
at okhttp3.internal.connection.RealCall$AsyncCall.run(RealCall.kt:519) [okhttp-4.11.0.jar:na]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_332]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_332]
at java.lang.Thread.run(Thread.java:750) [na:1.8.0_332]

To Reproduce

1. create your model ,like this:

public static StreamingChatLanguageModel createStreamingChatLanguageMode(String mode, int maxToken) {
        return OpenAiStreamingChatModel.builder()
                .baseUrl(moonshot_url)
                .apiKey(moonshot_api_key)
                .modelName(mode)
                .logRequests(true)//open log request 
                .temperature(temperature)
                .maxTokens(maxToken)
                .build();
    }

2. declare your services, like :

public interface IChatAgent  {

    // use TokenStream 
    TokenStream chat( String question);

}

3. create AiService :

 IChatAgent chatAgent = AiServices.builder(IChatAgent.class)
                .streamingChatLanguageModel(chatModel)
                .chatMemory(MessageWindowChatMemory.withMaxMessages(5))
                .build();

4. start token steam ,like this:

 chatAgent.chat( result.getInput())
                        .onNext(text -> {
                            try {
                                emitter.send(
                                        collector.append(text).toString(), MediaType.TEXT_PLAIN);
                            } catch (IOException e) {
                                e.printStackTrace();
                            }
                        }).onComplete(messageResponse -> emitter.complete())
                        .onError(emitter::completeWithError)
                        .start();

1. than you will see this bug in your log .
2. if close logRequests , NullPointerException disappear ；
   Expected behavior

fix this bug , or allow custom TokenStream ;

Please complete the following information:

• LangChain4j version: 0.29.1
• LLM(s) used: moonshot_v1_8k
• Java version: JDK 1.8
• Spring Boot version (if applicable):
  implementation 'org.springframework.boot:spring-boot-starter-web'

Additional context

[langchain4j]

This happends with other models as well:

java.lang.NullPointerException: Cannot read field "inputTokenCount" because "that" is null
	at dev.langchain4j.model.output.TokenUsage.add(TokenUsage.java:88) ~[langchain4j-core-0.29.1.jar:na]
	at dev.langchain4j.service.AiServiceStreamingResponseHandler.onComplete(AiServiceStreamingResponseHandler.java:92) ~[langchain4j-0.29.1.jar:na]
	at dev.langchain4j.model.azure.AzureOpenAiStreamingChatModel.generate(AzureOpenAiStreamingChatModel.java:278) ~[langchain4j-azure-open-ai-0.29.1.jar:na]
	at dev.langchain4j.model.azure.AzureOpenAiStreamingChatModel.generate(AzureOpenAiStreamingChatModel.java:223) ~[langchain4j-azure-open-ai-0.29.1.jar:na]
	at dev.langchain4j.service.AiServiceTokenStream$AiServiceOnStart.start(AiServiceTokenStream.java:88) ~[langchain4j-0.29.1.jar:na]

[hehr]

OK，I have updated v0.30 ；