[Bug]: NullPointerException in A2ACommonFieldMapper when a struct field has an explicit null value

Bắt đầu trong A2ACommonFieldMapper.structToMap và valueToObject, sau đó lần theo đường dẫn TaskMapperImpl/MessageMapperImpl được Client.getTask(...) gọi tới qua JSON-RPC. Hoàn tất khi một phản hồi chứa các trường null tường minh lồng nhau được chuyển đổi mà không xảy ra NullPointerException và các trường null vẫn được biểu diễn trong dữ liệu kết quả.

What happened?

A2ACommonFieldMapper.structToMap throws a NullPointerException when converting a protobuf Struct that contains a field whose value is an explicit JSON null (protobuf Value.KindCase.NULL_VALUE). This reproduces on 1.3.0.Final when deserializing a Task returned from GetTask, specifically when a message part's structured data contains a null field anywhere in its (possibly nested) object.

This looks like an incomplete fix of #618: that issue fixed the empty-struct case (valueToObject now short-circuits STRUCT_VALUE with 0 fields to Collections.emptyMap() — see lines 218-224 in the current source), but the explicit-null-field case was not addressed and still NPEs.

Root Cause

valueToObject correctly returns Java null for a protobuf NULL_VALUE field:

  case NULL_VALUE:                                                                                                                                                                                                                                                            
  default:                                                                                                                                                                                                                                                                    
      return null;                                                                                                                                                                                                                                                            

But structToMap collects the struct's fields with Collectors.toMap:

  default Map<String, Object> structToMap(Struct struct) {                                                                                                                                                                                                                    
      if (struct == null || struct.getFieldsCount() == 0) {                                                                                                                                                                                                                   
          return null;                                                                                                                                                                                                                                                        
      }                                                                                                                                                                                                                                                                       
      return struct.getFieldsMap().entrySet().stream()                                                                                                                                                                                                                        
              .collect(Collectors.toMap(Map.Entry::getKey, e -> valueToObject(e.getValue())));                                                                                                                                                                                
  }

Collectors.toMap's default accumulator calls Map.merge, which calls Objects.requireNonNull(value) — it cannot accept a null mapped value, regardless of how deeply nested the offending field is. Any JSON object with a null field anywhere in a message's structured data part therefore breaks task/message deserialization entirely.

Steps to Reproduce

1. Have a server return (via GetTask, or any response going through TaskMapperImpl/MessageMapperImpl) a message part whose structured JSON data contains an explicit null field, e.g.:

  {                                                                                                                                                                                                                                                                           
    "data": {                                                                                                                                                                                                                                                                 
      "data": {                                                                                                                                                                                                                                                               
        "some_optional_field": null,                                                                                                                                                                                                                                          
        "other_field": "value"                                                                                                                                                                                                                                                
      }                                                                                                                                                                                                                                                                       
    }                                                                                                                                                                                                                                                                         
  }

2. Have the client call Client.getTask(...) (JSON-RPC transport) to fetch that task.
3. A NullPointerException is thrown while converting the response, and the client never gets to see the actual task/message content.

Relevant log output

java.lang.NullPointerException
	at java.base/java.util.Objects.requireNonNull(Objects.java:233)
	at java.base/java.util.stream.Collectors.lambda$uniqKeysMapAccumulator$1(Collectors.java:180)
	at java.base/java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java:169)
	at java.base/java.util.Collections$UnmodifiableMap$UnmodifiableEntrySet.lambda$entryConsumer$0(Collections.java:1778)
	at java.base/java.util.Iterator.forEachRemaining(Iterator.java:133)
	at java.base/java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1939)
	at java.base/java.util.Collections$UnmodifiableMap$UnmodifiableEntrySet$UnmodifiableEntrySetSpliterator.forEachRemaining(Collections.java:1803)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499)
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:921)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:682)
	at org.a2aproject.sdk.grpc.mapper.A2ACommonFieldMapper.structToMap(A2ACommonFieldMapper.java:170)
	at org.a2aproject.sdk.grpc.mapper.A2ACommonFieldMapper.valueToObject(A2ACommonFieldMapper.java:225)
	at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:197)
	at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1708)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499)
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:921)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:682)
	at org.a2aproject.sdk.grpc.mapper.A2ACommonFieldMapper.valueToObject(A2ACommonFieldMapper.java:229)
	at org.a2aproject.sdk.grpc.mapper.A2ACommonFieldMapper.lambda$structToMap$1(A2ACommonFieldMapper.java:170)
	at java.base/java.util.stream.Collectors.lambda$uniqKeysMapAccumulator$1(Collectors.java:180)
	at java.base/java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java:169)
	at java.base/java.util.Collections$UnmodifiableMap$UnmodifiableEntrySet.lambda$entryConsumer$0(Collections.java:1778)
	at java.base/java.util.Iterator.forEachRemaining(Iterator.java:133)
	at java.base/java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1939)
	at java.base/java.util.Collections$UnmodifiableMap$UnmodifiableEntrySet$UnmodifiableEntrySetSpliterator.forEachRemaining(Collections.java:1803)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499)
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:921)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:682)
	at org.a2aproject.sdk.grpc.mapper.A2ACommonFieldMapper.structToMap(A2ACommonFieldMapper.java:170)
	at org.a2aproject.sdk.grpc.mapper.A2ACommonFieldMapper.valueToObject(A2ACommonFieldMapper.java:225)
	at org.a2aproject.sdk.grpc.mapper.A2ACommonFieldMapper.lambda$structToMap$1(A2ACommonFieldMapper.java:170)
	at java.base/java.util.stream.Collectors.lambda$uniqKeysMapAccumulator$1(Collectors.java:180)
	at java.base/java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java:169)
	at java.base/java.util.Collections$UnmodifiableMap$UnmodifiableEntrySet.lambda$entryConsumer$0(Collections.java:1778)
	at java.base/java.util.Iterator.forEachRemaining(Iterator.java:133)
	at java.base/java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1939)
	at java.base/java.util.Collections$UnmodifiableMap$UnmodifiableEntrySet$UnmodifiableEntrySetSpliterator.forEachRemaining(Collections.java:1803)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499)
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:921)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:682)
	at org.a2aproject.sdk.grpc.mapper.A2ACommonFieldMapper.structToMap(A2ACommonFieldMapper.java:170)
	at org.a2aproject.sdk.grpc.mapper.A2ACommonFieldMapper.valueToObject(A2ACommonFieldMapper.java:225)
	at org.a2aproject.sdk.grpc.mapper.A2ACommonFieldMapper.lambda$structToMap$1(A2ACommonFieldMapper.java:170)
	at java.base/java.util.stream.Collectors.lambda$uniqKeysMapAccumulator$1(Collectors.java:180)
	at java.base/java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java:169)
	at java.base/java.util.Collections$UnmodifiableMap$UnmodifiableEntrySet.lambda$entryConsumer$0(Collections.java:1778)
	at java.base/java.util.Iterator.forEachRemaining(Iterator.java:133)
	at java.base/java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1939)
	at java.base/java.util.Collections$UnmodifiableMap$UnmodifiableEntrySet$UnmodifiableEntrySetSpliterator.forEachRemaining(Collections.java:1803)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499)
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:921)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:682)
	at org.a2aproject.sdk.grpc.mapper.A2ACommonFieldMapper.structToMap(A2ACommonFieldMapper.java:170)
	at org.a2aproject.sdk.grpc.mapper.A2ACommonFieldMapper.valueToObject(A2ACommonFieldMapper.java:225)
	at org.a2aproject.sdk.grpc.mapper.PartMapper.fromProto(PartMapper.java:110)
	at org.a2aproject.sdk.grpc.mapper.MessageMapperImpl.partListToPartArray(MessageMapperImpl.java:88)
	at org.a2aproject.sdk.grpc.mapper.MessageMapperImpl.fromProto(MessageMapperImpl.java:72)
	at org.a2aproject.sdk.grpc.mapper.TaskMapperImpl.messageListToMessageArray(TaskMapperImpl.java:95)
	at org.a2aproject.sdk.grpc.mapper.TaskMapperImpl.fromProto(TaskMapperImpl.java:69)
	at org.a2aproject.sdk.grpc.utils.ProtoUtils$FromProto.lambda$task$11(ProtoUtils.java:313)
	at org.a2aproject.sdk.grpc.utils.ProtoUtils$FromProto.convert(ProtoUtils.java:198)
	at org.a2aproject.sdk.grpc.utils.ProtoUtils$FromProto.task(ProtoUtils.java:313)
	at org.a2aproject.sdk.grpc.utils.JSONRPCUtils.parseResponseBody(JSONRPCUtils.java:315)
	at org.a2aproject.sdk.client.transport.jsonrpc.JSONRPCTransport.unmarshalResponse(JSONRPCTransport.java:369)
	at org.a2aproject.sdk.client.transport.jsonrpc.JSONRPCTransport.getTask(JSONRPCTransport.java:148)
	at org.a2aproject.sdk.client.Client.getTask(Client.java:371)
(application code)

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