DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES does not work correctly

[bantu]

Context

We are making HTTP requests from a Spring Boot 3.4.6 application using WebFlux WebClient with HAL enabled.

Problem

Deserialization only works when all fields from the HTTP response are present in the Model specified in ParameterizedTypeReference. We are seeing the following exception when a field is missing. Based on the fact that DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES is disabled throughout the codebase, this is unexpected.

org.springframework.core.codec.DecodingException: JSON decoding error: Cannot invoke "com.fasterxml.jackson.databind.JsonDeserializer.deserialize(com.fasterxml.jackson.core.JsonParser, com.fasterxml.jackson.databind.DeserializationContext)" because "this._valueDeserializer" is null
        at org.springframework.http.codec.json.AbstractJackson2Decoder.processException(AbstractJackson2Decoder.java:282) ~[spring-web-6.2.7.jar:6.2.7]
        Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: 
Error has been observed at the following site(s):
        *__checkpoint ⇢ Body from GET https://XXX/YYY [DefaultClientResponse]
Original Stack Trace:
                at org.springframework.http.codec.json.AbstractJackson2Decoder.processException(AbstractJackson2Decoder.java:282) ~[spring-web-6.2.7.jar:6.2.7]
                at org.springframework.http.codec.json.AbstractJackson2Decoder.decode(AbstractJackson2Decoder.java:218) ~[spring-web-6.2.7.jar:6.2.7]
                at org.springframework.http.codec.json.AbstractJackson2Decoder.lambda$decodeToMono$2(AbstractJackson2Decoder.java:198) ~[spring-web-6.2.7.jar:6.2.7]
                at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:132) ~[reactor-core-3.7.6.jar:3.7.6]
                at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.onNext(FluxContextWrite.java:107) ~[reactor-core-3.7.6.jar:3.7.6]
                at reactor.core.publisher.FluxMapFuseable$MapFuseableConditionalSubscriber.onNext(FluxMapFuseable.java:299) ~[reactor-core-3.7.6.jar:3.7.6]
                at reactor.core.publisher.FluxFilterFuseable$FilterFuseableConditionalSubscriber.onNext(FluxFilterFuseable.java:337) ~[reactor-core-3.7.6.jar:3.7.6]
                at reactor.core.publisher.Operators$BaseFluxToMonoOperator.completePossiblyEmpty(Operators.java:2096) ~[reactor-core-3.7.6.jar:3.7.6]
                at reactor.core.publisher.MonoCollect$CollectSubscriber.onComplete(MonoCollect.java:145) ~[reactor-core-3.7.6.jar:3.7.6]
                at reactor.core.publisher.FluxMap$MapSubscriber.onComplete(FluxMap.java:144) ~[reactor-core-3.7.6.jar:3.7.6]
                at reactor.core.publisher.FluxPeek$PeekSubscriber.onComplete(FluxPeek.java:260) ~[reactor-core-3.7.6.jar:3.7.6]
                at reactor.core.publisher.FluxMap$MapSubscriber.onComplete(FluxMap.java:144) ~[reactor-core-3.7.6.jar:3.7.6]
                at reactor.netty.channel.FluxReceive.onInboundComplete(FluxReceive.java:413) ~[reactor-netty-core-1.2.6.jar:1.2.6]
                at reactor.netty.channel.ChannelOperations.onInboundComplete(ChannelOperations.java:455) ~[reactor-netty-core-1.2.6.jar:1.2.6]
                at reactor.netty.channel.ChannelOperations.terminate(ChannelOperations.java:509) ~[reactor-netty-core-1.2.6.jar:1.2.6]
                at reactor.netty.http.client.HttpClientOperations.onInboundNext(HttpClientOperations.java:821) ~[reactor-netty-http-1.2.6.jar:1.2.6]
                at reactor.netty.channel.ChannelOperationsHandler.channelRead(ChannelOperationsHandler.java:115) ~[reactor-netty-core-1.2.6.jar:1.2.6]
                at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:436) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:346) ~[netty-codec-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:318) ~[netty-codec-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:251) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:442) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.handler.logging.LoggingHandler.channelRead(LoggingHandler.java:280) ~[netty-handler-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:442) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.handler.ssl.SslHandler.unwrap(SslHandler.java:1519) ~[netty-handler-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.handler.ssl.SslHandler.decodeJdkCompatible(SslHandler.java:1377) ~[netty-handler-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.handler.ssl.SslHandler.decode(SslHandler.java:1428) ~[netty-handler-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:530) ~[netty-codec-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:469) ~[netty-codec-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:290) ~[netty-codec-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1357) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:440) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:868) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:799) ~[netty-transport-classes-epoll-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.epoll.EpollEventLoop.processReady(EpollEventLoop.java:501) ~[netty-transport-classes-epoll-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:399) ~[netty-transport-classes-epoll-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:998) ~[netty-common-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) ~[netty-common-4.1.121.Final.jar:4.1.121.Final]
                at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) ~[netty-common-4.1.121.Final.jar:4.1.121.Final]
                at java.base/java.lang.Thread.run(Thread.java:840) ~[na:na]
        Suppressed: java.lang.Exception: #block terminated with an error
                at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:104) ~[reactor-core-3.7.6.jar:3.7.6]
                at reactor.core.publisher.Mono.block(Mono.java:1779) ~[reactor-core-3.7.6.jar:3.7.6]
                at [XXX](MetadataUpdatedSyncListener.java:75) ~[main/:na]
                at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
                at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77) ~[na:na]
                at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
                at java.base/java.lang.reflect.Method.invoke(Method.java:569) ~[na:na]
                at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:359) ~[spring-aop-6.2.7.jar:6.2.7]
                at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:196) ~[spring-aop-6.2.7.jar:6.2.7]
                at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) ~[spring-aop-6.2.7.jar:6.2.7]
                at org.springframework.aop.interceptor.AsyncExecutionInterceptor.lambda$invoke$0(AsyncExecutionInterceptor.java:114) ~[spring-aop-6.2.7.jar:6.2.7]
                at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) ~[na:na]
                at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136) ~[na:na]
                at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635) ~[na:na]
                at java.base/java.lang.Thread.run(Thread.java:840) ~[na:na]
Caused by: com.fasterxml.jackson.databind.JsonMappingException: Cannot invoke "com.fasterxml.jackson.databind.JsonDeserializer.deserialize(com.fasterxml.jackson.core.JsonParser, com.fasterxml.jackson.databind.DeserializationContext)" because "this._valueDeserializer" is null (through reference chain: org.springframework.hateoas.CollectionModel["_embedded"]->XXX.dto.SiteModel["bar"])
        at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:401) ~[jackson-databind-2.18.4.jar:2.18.4]
        at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:360) ~[jackson-databind-2.18.4.jar:2.18.4]
        at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.wrapAndThrow(BeanDeserializerBase.java:1964) ~[jackson-databind-2.18.4.jar:2.18.4]
        at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownVanilla(BeanDeserializerBase.java:1795) ~[jackson-databind-2.18.4.jar:2.18.4]
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:405) ~[jackson-databind-2.18.4.jar:2.18.4]
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:185) ~[jackson-databind-2.18.4.jar:2.18.4]
        at com.fasterxml.jackson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:138) ~[jackson-databind-2.18.4.jar:2.18.4]
        at com.fasterxml.jackson.databind.deser.impl.UnwrappedPropertyHandler.processUnwrapped(UnwrappedPropertyHandler.java:63) ~[jackson-databind-2.18.4.jar:2.18.4]
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeWithUnwrapped(BeanDeserializer.java:787) ~[jackson-databind-2.18.4.jar:2.18.4]
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:343) ~[jackson-databind-2.18.4.jar:2.18.4]
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:185) ~[jackson-databind-2.18.4.jar:2.18.4]
        at org.springframework.hateoas.mediatype.hal.Jackson2HalModule$HalResourcesDeserializer.deserialize(Jackson2HalModule.java:677) ~[spring-hateoas-2.4.1.jar:2.4.1]
        at org.springframework.hateoas.mediatype.hal.Jackson2HalModule$HalResourcesDeserializer.deserialize(Jackson2HalModule.java:615) ~[spring-hateoas-2.4.1.jar:2.4.1]
        at com.fasterxml.jackson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:138) ~[jackson-databind-2.18.4.jar:2.18.4]
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:399) ~[jackson-databind-2.18.4.jar:2.18.4]
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:185) ~[jackson-databind-2.18.4.jar:2.18.4]
        at com.fasterxml.jackson.databind.deser.DefaultDeserializationContext.readRootValue(DefaultDeserializationContext.java:342) ~[jackson-databind-2.18.4.jar:2.18.4]
        at com.fasterxml.jackson.databind.ObjectReader._bindAndClose(ObjectReader.java:2131) ~[jackson-databind-2.18.4.jar:2.18.4]
        at com.fasterxml.jackson.databind.ObjectReader.readValue(ObjectReader.java:1501) ~[jackson-databind-2.18.4.jar:2.18.4]
        at org.springframework.http.codec.json.AbstractJackson2Decoder.decode(AbstractJackson2Decoder.java:213) ~[spring-web-6.2.7.jar:6.2.7]
        at org.springframework.http.codec.json.AbstractJackson2Decoder.lambda$decodeToMono$2(AbstractJackson2Decoder.java:198) ~[spring-web-6.2.7.jar:6.2.7]
        at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:132) ~[reactor-core-3.7.6.jar:3.7.6]
        at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.onNext(FluxContextWrite.java:107) ~[reactor-core-3.7.6.jar:3.7.6]
        at reactor.core.publisher.FluxMapFuseable$MapFuseableConditionalSubscriber.onNext(FluxMapFuseable.java:299) ~[reactor-core-3.7.6.jar:3.7.6]
        at reactor.core.publisher.FluxFilterFuseable$FilterFuseableConditionalSubscriber.onNext(FluxFilterFuseable.java:337) ~[reactor-core-3.7.6.jar:3.7.6]
        at reactor.core.publisher.Operators$BaseFluxToMonoOperator.completePossiblyEmpty(Operators.java:2096) ~[reactor-core-3.7.6.jar:3.7.6]
        at reactor.core.publisher.MonoCollect$CollectSubscriber.onComplete(MonoCollect.java:145) ~[reactor-core-3.7.6.jar:3.7.6]
        at reactor.core.publisher.FluxMap$MapSubscriber.onComplete(FluxMap.java:144) ~[reactor-core-3.7.6.jar:3.7.6]
        at reactor.core.publisher.FluxPeek$PeekSubscriber.onComplete(FluxPeek.java:260) ~[reactor-core-3.7.6.jar:3.7.6]
        at reactor.core.publisher.FluxMap$MapSubscriber.onComplete(FluxMap.java:144) ~[reactor-core-3.7.6.jar:3.7.6]
        at reactor.netty.channel.FluxReceive.onInboundComplete(FluxReceive.java:413) ~[reactor-netty-core-1.2.6.jar:1.2.6]
        at reactor.netty.channel.ChannelOperations.onInboundComplete(ChannelOperations.java:455) ~[reactor-netty-core-1.2.6.jar:1.2.6]
        at reactor.netty.channel.ChannelOperations.terminate(ChannelOperations.java:509) ~[reactor-netty-core-1.2.6.jar:1.2.6]
        at reactor.netty.http.client.HttpClientOperations.onInboundNext(HttpClientOperations.java:821) ~[reactor-netty-http-1.2.6.jar:1.2.6]
        at reactor.netty.channel.ChannelOperationsHandler.channelRead(ChannelOperationsHandler.java:115) ~[reactor-netty-core-1.2.6.jar:1.2.6]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:436) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:346) ~[netty-codec-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:318) ~[netty-codec-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:251) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:442) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.handler.logging.LoggingHandler.channelRead(LoggingHandler.java:280) ~[netty-handler-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:442) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.handler.ssl.SslHandler.unwrap(SslHandler.java:1519) ~[netty-handler-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.handler.ssl.SslHandler.decodeJdkCompatible(SslHandler.java:1377) ~[netty-handler-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.handler.ssl.SslHandler.decode(SslHandler.java:1428) ~[netty-handler-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:530) ~[netty-codec-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:469) ~[netty-codec-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:290) ~[netty-codec-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1357) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:440) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:868) ~[netty-transport-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:799) ~[netty-transport-classes-epoll-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.epoll.EpollEventLoop.processReady(EpollEventLoop.java:501) ~[netty-transport-classes-epoll-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:399) ~[netty-transport-classes-epoll-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:998) ~[netty-common-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) ~[netty-common-4.1.121.Final.jar:4.1.121.Final]
        at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) ~[netty-common-4.1.121.Final.jar:4.1.121.Final]
        at java.base/java.lang.Thread.run(Thread.java:840) ~[na:na]
Caused by: java.lang.NullPointerException: Cannot invoke "com.fasterxml.jackson.databind.JsonDeserializer.deserialize(com.fasterxml.jackson.core.JsonParser, com.fasterxml.jackson.databind.DeserializationContext)" because "this._valueDeserializer" is null
        at com.fasterxml.jackson.databind.deser.SettableAnyProperty.deserialize(SettableAnyProperty.java:256) ~[jackson-databind-2.18.4.jar:2.18.4]
        at com.fasterxml.jackson.databind.deser.SettableAnyProperty.deserializeAndSet(SettableAnyProperty.java:237) ~[jackson-databind-2.18.4.jar:2.18.4]
        at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownVanilla(BeanDeserializerBase.java:1793) ~[jackson-databind-2.18.4.jar:2.18.4]
        ... 65 common frames omitted

Additional information

build.gradle

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-amqp'
    implementation 'org.springframework.boot:spring-boot-starter-json'
    implementation 'org.springframework.boot:spring-boot-starter-webflux'
    implementation 'org.springframework.hateoas:spring-hateoas'
    implementation 'org.springframework.boot:spring-boot-starter-data-rest'
}

BackendWebClientConfiguration.java

@EnableHypermediaSupport(type = HypermediaType.HAL)
@Configuration
public class BackendWebClientConfiguration {
    @Bean
    WebClient chargeStackBackendWebClient(
        WebClient.Builder builder,
        @Value("${backend.uri}") String backendUri,
        @Value("${backend.username:}") String username,
        @Value("${backend.password:}") String password
    ) {
        HttpClient httpClient = HttpClient
            .create()
            .wiretap("reactor.netty.http.client.HttpClient", LogLevel.DEBUG, AdvancedByteBufFormat.TEXTUAL)
        ;
        WebClient.Builder b = builder
            .clientConnector(new ReactorClientHttpConnector(httpClient))
            .baseUrl(backendUri)
            .defaultHeader(HttpHeaders.ACCEPT, MediaTypes.HAL_JSON_VALUE)
        ;
        if (!username.isEmpty() && !password.isEmpty()) {
            b = b.defaultHeaders(header -> header.setBasicAuth(username, password));
        }
        return b.build();
    }
}

SiteModel.java

public class SiteModel extends EntityModel<SiteModel> {
    public UUID uuid;
    public String name;
    public String foo;
    // Missing
    // public String bar; 
}

Request

webClient
            .get()
            .uri("/{id}/sites", id)
            .retrieve()
            .bodyToMono(new ParameterizedTypeReference<CollectionModel<SiteModel>>() {})
            .doOnSuccess(x -> log.info("{}", x))
            .block()
        ;

[odrotbohm]

The exception seems to be coming from within Jackson. So I guess the ticket would need to be filed with it?

[bantu]

The exception seems to be coming from within Jackson. So I guess the ticket would need to be filed with it?

@odrotbohm It is my understanding _valueDeserializer being null is caused by some infrastructure (Decoder?) registered by spring-hateoas with Jackson for HAL-support.

[odrotbohm]

While we certainly do that, there's no evidence here so far that this problem here is caused by that. Any chance you prepare a reproducer that contains a failing test?