Hyperledger Fabric GetHistoryForKey get null pointer exception on java

I have the fabric samples project. I modified one of the examples there to experiment. I enabled couchDB and try to get the history of transactions. in core.yaml i enabled the history.

   @Transaction(intent = Transaction.TYPE.EVALUATE)
public ArrayList<String> GetAssetHistory(final Context ctx, final String assetID) {
    ChaincodeStub stub = ctx.getStub();
    ArrayList<String> results = new ArrayList<>();
    try {
        QueryResultsIterator<KeyModification> history = stub.getHistoryForKey(assetID);

        Iterator<KeyModification> iter = history.iterator();
        while(iter.hasNext()){
                results.add(iter.next().getStringValue());
        }
    }
    catch(Exception e){
        results.add(e.getMessage());
        results.add(e.getCause().getMessage());
        results.add(e.getStackTrace().toString());
    }
    return results;
}

If i run my app that uses the new method in contract i get org.hyperledger.fabric.gateway.ContractException: error in simulation: transaction returned with failure: Unexpected error in the intellij terminal. I checked different dockers logs. org1.example.com has the same error. But the peer0.org1.... docker has a but more informative exception.

15:41:31:432 SEVERE  org.hyperledger.fabric.Logger error                                              nulljava.lang.NullPointerException
    at org.hyperledger.fabric.contract.execution.JSONTransactionSerializer.toBuffer(JSONTransactionSerializer.java:84)
    at org.hyperledger.fabric.contract.execution.impl.ContractExecutionService.convertReturn(ContractExecutionService.java:89)
    at org.hyperledger.fabric.contract.execution.impl.ContractExecutionService.executeRequest(ContractExecutionService.java:67)
    at org.hyperledger.fabric.contract.ContractRouter.processRequest(ContractRouter.java:115)
    at org.hyperledger.fabric.contract.ContractRouter.invoke(ContractRouter.java:126)
    at org.hyperledger.fabric.shim.impl.ChaincodeInvocationTask.call(ChaincodeInvocationTask.java:91)
    at org.hyperledger.fabric.shim.impl.InvocationTaskManager.lambda$newTask$17(InvocationTaskManager.java:225)
    at java.base/java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1736)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at java.base/java.lang.Thread.run(Thread.java:834)

15:41:31:436 SEVERE  org.hyperledger.fabric.shim.impl.ChaincodeInvocationTask call                    [e0aa10de] Invoke failed with error code 500. Sending ERROR

Seems like the history is still not saved anywhere. Or its trying to communicate with some peer that does not exist.

I encountered the same issue and finally solved it by altering the return value of the function, in your case, from

public ArrayList<String> GetAssetHistory(final Context ctx, final String assetID)

to

public String GetAssetHistory(final Context ctx, final String assetID)

If you look into this class org.hyperledger.fabric.contract.execution.JSONTransactionSerializer at Github, you could find the function toBuffer convert types to json.

Here is a stripped version:

public byte[] toBuffer(final Object value, final TypeSchema ts) {
    final String type = ts.getType();
    if (type != null) {
        switch (type) {
        case "array":
            ...
        case "string":
            ...
        case "number":
        case "integer":
        case "boolean":
        default:
            ...
        }
    } else {
        // at this point we can assert that the value is
        // representing a complex data type
        // so we can get this from
        // the type registry, and get the list of propertyNames
        // it should have
        final DataTypeDefinition dtd = this.typeRegistry.getDataType(ts);
        final Set<String> keySet = dtd.getProperties().keySet();
        ...
    }
}

In my code I didn't use ArrayList but a customized type, so it would go to else directly. But in your code I don't know if the ArrayList would go into if as a array or it would be interpreted as a customized type. I guess it may go to else. So in else, ArrayList is not registered as a custom type via @DataType(), it would produce a NullPointerException.

So here I suggest you could just use String instead if works.

I faced the same issue. You need to implement a custom serializer for your chaincode. Refer to my blogpost https://thusithathilina.medium.com/how-to-register-a-custom-serializer-for-chaincode-in-hyperledger-fabric-9e865f6d68d0

Steps

1. Implement the SerializerInterface and provide an implementation for toBuffer method to convert your ArrayList to a byte[]
2. Register your serializer with the contract using transactionSerializer attribute inside @Contract annotation