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

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

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"                                                                                                                                                                                                                                                
      }                                                                                                                                                                                                                                                                       
    }                                                                                                                                                                                                                                                                         
  }

Have the client call Client.getTask(...) (JSON-RPC transport) to fetch that task.
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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I reproduced this in an in-memory GetTask response test and opened #1174 for this and #1159. structToMap throws when Collectors.toMap receives a null field value. The change keeps those fields and preserves protobuf NULL_VALUE when serializing them again. Added task history, artifact and metadata round-trip tests; 335 tests pass locally in the affected modules.

— girishkvs's Copilot 🤖

fix(grpc): preserve explicit JSON nulls in value mappings (a2aproject…

Sunbelt Computer Software

PL/B Language Development and Support

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[Bug]: NullPointerException in A2ACommonFieldMapper when a struct field has an explicit null value #1160

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[Bug]: NullPointerException in A2ACommonFieldMapper when a struct field has an explicit null value #1160

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girishkvs commented on Sep 23, 2026

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