Fix an error on eth_subscribe deserializing the block

[jframe]

PR description

Fixes a Json decoding error on eth_subscribe by using a Jackson mapper with jdk8 support. This is due to the addition of Optional<BlockAccessListResult> on the BlockResult.

I've created a Jackson mapper in the SubscriptionManager to use instead of using the vertx Json library. It would be ideal to pass in Jackson mapper instead but there didn't seem to be one readably available where the SubscriptionManager is created.

This is the error we get:

2025-09-23 05:07:05.572+0000 | vert.x-eventloop-thread-7 | ERROR | SubscriptionManager | Failed to notify subscribers.                                                                                                             
io.vertx.core.json.EncodeException: Failed to encode as JSON: Java 8 optional type `java.util.Optional<org.hyperledger.besu.ethereum.api.jsonrpc.internal.results.BlockAccessListResult>` not supported by default: add Module "com
.fasterxml.jackson.datatype:jackson-datatype-jdk8" to enable handling (through reference chain: org.hyperledger.besu.ethereum.api.jsonrpc.websocket.subscription.response.SubscriptionResponse["params"]->org.hyperledger.besu.ethe
reum.api.jsonrpc.websocket.subscription.response.SubscriptionResponseResult["result"]->org.hyperledger.besu.ethereum.api.jsonrpc.internal.results.BlockResult["blockAccessList"])                                                  
    at io.vertx.core.json.jackson.DatabindCodec.toString(DatabindCodec.java:167)

Fixed Issue(s)

Thanks for sending a pull request! Have you done the following?

• Checked out our contribution guidelines?
• Considered documentation and added the doc-change-required label to this PR if updates are required.
• Considered the changelog and included an update if required.
• For database changes (e.g. KeyValueSegmentIdentifier) considered compatibility and performed forwards and backwards compatibility tests

Locally, you can run these tests to catch failures early:

• spotless: ./gradlew spotlessApply
• unit tests: ./gradlew build
• acceptance tests: ./gradlew acceptanceTest
• integration tests: ./gradlew integrationTest
• reference tests: ./gradlew ethereum:referenceTests:referenceTests
• hive tests: Engine or other RPCs modified?

…

Signed-off-by: Jason Frame jason.frame@consensys.net

[matkt]

LGTM

[macfarla]

related fix #9220