Spring-ai Anthropic streaming error: NullPointerException

Bug description NullPointerException happens during anthropic streaming

Aggregation Error
java.lang.NullPointerException: Cannot invoke "org.springframework.ai.anthropic.api.StreamHelper$ChatCompletionResponseBuilder.withType(String)" because the return value of "java.util.concurrent.atomic.AtomicReference.get()" is null

Environment "org.springframework.ai:spring-ai-bom:1.0.0-SNAPSHOT + org.springframework.ai:spring-ai-openai + org.springframework.ai:spring-ai-anthropic-spring-boot-starter

Steps to reproduce Unfortunately, it happens sometimes, probably it depends on the streaming response chain. Prerequisites: Anthropic streaming call

org.springframework.ai.chat.model.MessageAggregator:170 lambda$aggregate$6 - Aggregation Error

 java.lang.NullPointerException: Cannot invoke "org.springframework.ai.anthropic.api.StreamHelper$ChatCompletionResponseBuilder.withType(String)" because the return value of "java.util.concurrent.atomic.AtomicReference.get()" is null
         at org.springframework.ai.anthropic.api.StreamHelper.eventToChatCompletionResponse(StreamHelper.java:185)
         at org.springframework.ai.anthropic.api.AnthropicApi.lambda$chatCompletionStream$9(AnthropicApi.java:217)
         at reactor.core.publisher.FluxMap$MapConditionalSubscriber.onNext(FluxMap.java:208)
         at reactor.core.publisher.FluxFlatMap$FlatMapMain.tryEmit(FluxFlatMap.java:547)
         at reactor.core.publisher.FluxFlatMap$FlatMapInner.onNext(FluxFlatMap.java:988)
         at reactor.core.publisher.Operators$BaseFluxToMonoOperator.completePossiblyEmpty(Operators.java:2097)
         at reactor.core.publisher.MonoReduceSeed$ReduceSeedSubscriber.onComplete(MonoReduceSeed.java:163)
         at reactor.core.publisher.FluxWindowPredicate$WindowFlux.checkTerminated(FluxWindowPredicate.java:768)
         at reactor.core.publisher.FluxWindowPredicate$WindowFlux.drainRegular(FluxWindowPredicate.java:662)
         at reactor.core.publisher.FluxWindowPredicate$WindowFlux.drain(FluxWindowPredicate.java:748)
         at reactor.core.publisher.FluxWindowPredicate$WindowFlux.onComplete(FluxWindowPredicate.java:814)
         at reactor.core.publisher.FluxWindowPredicate$WindowPredicateMain.onNext(FluxWindowPredicate.java:243)
         at reactor.core.publisher.FluxMap$MapSubscriber.onNext(FluxMap.java:122)
         at reactor.core.publisher.FluxFilter$FilterSubscriber.onNext(FluxFilter.java:113)
         at reactor.core.publisher.FluxMap$MapConditionalSubscriber.onNext(FluxMap.java:224)
         at reactor.core.publisher.FluxFilter$FilterConditionalSubscriber.onNext(FluxFilter.java:247)
         at reactor.core.publisher.FluxTakeUntil$TakeUntilPredicateSubscriber.onNext(FluxTakeUntil.java:95)
         at reactor.core.publisher.MonoFlatMapMany$FlatMapManyInner.onNext(MonoFlatMapMany.java:251)
         at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onNext(FluxOnErrorResume.java:79)
         at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.onNext(FluxOnAssembly.java:539)
         at reactor.core.publisher.FluxConcatMapNoPrefetch$FluxConcatMapNoPrefetchSubscriber.innerNext(FluxConcatMapNoPrefetch.java:259)
         at reactor.core.publisher.FluxConcatMap$ConcatMapInner.onNext(FluxConcatMap.java:865)
         at reactor.core.publisher.FluxConcatMap$WeakScalarSubscription.request(FluxConcatMap.java:480)
         at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.set(Operators.java:2367)