`java.lang.NullPointerException: null` when suspending despite `@Suspendable`

See https://github.com/corda/cordapp-example/tree/joel-bug-branch.

The flow is defined in Java as follows:

package com.example.flow;

import co.paralleluniverse.fibers.Suspendable;
import com.google.common.collect.ImmutableList;
import kotlin.Triple;
import net.corda.core.flows.*;
import net.corda.core.identity.Party;

import java.util.List;

public class ExampleFlow {
    @InitiatingFlow
    @StartableByRPC
    public static class Initiator extends FlowLogic<Void> {
        private final Party otherParty;

        public Initiator(Party otherParty) {
            this.otherParty = otherParty;
        }

        @Suspendable
        @Override
        public Void call() throws FlowException {
            FlowSession otherPartySession = initiateFlow(otherParty);
            List<FlowSession> sessions = ImmutableList.of(otherPartySession);
            sessions.forEach( it -> sendAMessage(it, new Triple("a", "b", "c")));
            return null;
        }
    }

    @InitiatedBy(Initiator.class)
    public static class Acceptor extends FlowLogic<Void> {

        private final FlowSession otherPartyFlow;

        public Acceptor(FlowSession otherPartyFlow) {
            this.otherPartyFlow = otherPartyFlow;
        }

        @Suspendable
        @Override
        public Void call() throws FlowException {
            otherPartyFlow.receive(Triple.class).unwrap(it -> { return it; });
            return null;
        }
    }

    @Suspendable
    private static Void sendAMessage(FlowSession session, Triple t) {
        session.send(t);
        return null;
    }
}

Running it (e.g. by running the flow tests here: https://github.com/corda/cordapp-example/blob/joel-bug-branch/java-source/src/test/java/com/example/flow/IOUFlowTests.java) gives the following exception:

java.lang.NullPointerException: null
    at net.corda.node.services.statemachine.FlowStateMachineImpl.suspend(FlowStateMachineImpl.kt:514) ~[corda-node-3.2-corda.jar:?]
    at net.corda.node.services.statemachine.FlowStateMachineImpl.sendInternal(FlowStateMachineImpl.kt:370) ~[corda-node-3.2-corda.jar:?]
    at net.corda.node.services.statemachine.FlowStateMachineImpl.initiateSession(FlowStateMachineImpl.kt:434) ~[corda-node-3.2-corda.jar:?]
    at net.corda.node.services.statemachine.FlowStateMachineImpl.initiateSession$default(FlowStateMachineImpl.kt:423) ~[corda-node-3.2-corda.jar:?]
    at net.corda.node.services.statemachine.FlowStateMachineImpl.send(FlowStateMachineImpl.kt:246) ~[corda-node-3.2-corda.jar:?]
    at net.corda.node.services.statemachine.FlowSessionImpl.send(FlowSessionImpl.kt:52) ~[corda-node-3.2-corda.jar:?]
    at net.corda.node.services.statemachine.FlowSessionImpl.send(FlowSessionImpl.kt:56) ~[corda-node-3.2-corda.jar:?]
    at com.example.flow.ExampleFlow.sendAMessage(ExampleFlow.java:50) ~[classes/:?]
    at com.example.flow.ExampleFlow.access$000(ExampleFlow.java:11) ~[classes/:?]
    at com.example.flow.ExampleFlow$Initiator.lambda$call$0(ExampleFlow.java:26) ~[classes/:?]
    at com.google.common.collect.ImmutableList.forEach(ImmutableList.java:408) ~[guava-21.0.jar:?]
    at com.example.flow.ExampleFlow$Initiator.call(ExampleFlow.java:26) ~[classes/:?]
    at com.example.flow.ExampleFlow$Initiator.call(ExampleFlow.java:12) ~[classes/:?]
    at net.corda.node.services.statemachine.FlowStateMachineImpl.run(FlowStateMachineImpl.kt:96) [corda-node-3.2-corda.jar:?]
    at net.corda.node.services.statemachine.FlowStateMachineImpl.run(FlowStateMachineImpl.kt:44) [corda-node-3.2-corda.jar:?]
    at co.paralleluniverse.fibers.Fiber.run1(Fiber.java:1092) [quasar-core-0.7.9-jdk8.jar:0.7.9]
    at co.paralleluniverse.fibers.Fiber.exec(Fiber.java:788) [quasar-core-0.7.9-jdk8.jar:0.7.9]
    at co.paralleluniverse.fibers.RunnableFiberTask.doExec(RunnableFiberTask.java:100) [quasar-core-0.7.9-jdk8.jar:0.7.9]
    at co.paralleluniverse.fibers.RunnableFiberTask.run(RunnableFiberTask.java:91) [quasar-core-0.7.9-jdk8.jar:0.7.9]
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_171]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_171]
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) [?:1.8.0_171]
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) [?:1.8.0_171]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_171]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_171]
    at net.corda.node.utilities.AffinityExecutor$ServiceAffinityExecutor$1$thread$1.run(AffinityExecutor.kt:62) [corda-node-3.2-corda.jar:?]
[WARN ] 17:03:28,364 [Mock network] (StateMachineManagerImpl.kt:79) flow.[0f10b2ef-f456-4e28-9998-1b2a403c6caf].uncaughtException - Caught exception from flow {}
java.lang.IllegalStateException: Was expecting to find transaction set on current strand: Fiber@10000001:[0f10b2ef-f456-4e28-9998-1b2a403c6caf][task: co.paralleluniverse.fibers.RunnableFiberTask@12a75b63(Fiber@10000001), target: null, scheduler: net.corda.node.services.statemachine.StateMachineManagerImpl$FiberScheduler@3facca05]
    at net.corda.nodeapi.internal.persistence.DatabaseTransactionKt.getContextTransaction(DatabaseTransaction.kt:14) ~[corda-node-api-3.2-corda.jar:?]
    at net.corda.node.services.statemachine.FlowStateMachineImpl.rollbackTransaction$node(FlowStateMachineImpl.kt:151) ~[corda-node-3.2-corda.jar:?]
    at net.corda.node.services.statemachine.StateMachineManagerImpl$initFiber$3.invoke(StateMachineManagerImpl.kt:460) ~[corda-node-3.2-corda.jar:?]
    at net.corda.node.services.statemachine.StateMachineManagerImpl$initFiber$3.invoke(StateMachineManagerImpl.kt:63) ~[corda-node-3.2-corda.jar:?]
    at net.corda.node.services.statemachine.FlowStateMachineImpl.processException(FlowStateMachineImpl.kt:131) ~[corda-node-3.2-corda.jar:?]
    at net.corda.node.services.statemachine.FlowStateMachineImpl.run(FlowStateMachineImpl.kt:112) ~[corda-node-3.2-corda.jar:?]
    at net.corda.node.services.statemachine.FlowStateMachineImpl.run(FlowStateMachineImpl.kt:44) ~[corda-node-3.2-corda.jar:?]
    at co.paralleluniverse.fibers.Fiber.run1(Fiber.java:1092) [quasar-core-0.7.9-jdk8.jar:0.7.9]
    at co.paralleluniverse.fibers.Fiber.exec(Fiber.java:788) [quasar-core-0.7.9-jdk8.jar:0.7.9]
    at co.paralleluniverse.fibers.RunnableFiberTask.doExec(RunnableFiberTask.java:100) [quasar-core-0.7.9-jdk8.jar:0.7.9]
    at co.paralleluniverse.fibers.RunnableFiberTask.run(RunnableFiberTask.java:91) [quasar-core-0.7.9-jdk8.jar:0.7.9]
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_171]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_171]
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) [?:1.8.0_171]
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) [?:1.8.0_171]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_171]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_171]
    at net.corda.node.utilities.AffinityExecutor$ServiceAffinityExecutor$1$thread$1.run(AffinityExecutor.kt:62) [corda-node-3.2-corda.jar:?]

[keykey7]

I also face NPEs on a pure-java dapp during the suspend.

java.lang.NullPointerException
	at net.corda.node.services.statemachine.FlowStateMachineImpl.suspend(FlowStateMachineImpl.kt:380)
	at net.corda.node.services.statemachine.FlowSessionImpl.send(FlowSessionImpl.kt:78)
	at net.corda.node.services.statemachine.FlowSessionImpl.send(FlowSessionImpl.kt:82)

It’s not the first suspend within this flow. I can only reproduce it on a real multinode setup, but not with a multinode mock network. -Dco.paralleluniverse.fibers.verifyInstrumentation=true doesn’t complain nor does flowStackSnapshot() reveal any unexpected insights: there are no lambdas, unserializable classes, or alike in any frame. @lolo8304’s kotlin-project-hack didn’t help either. Any ideas on how to further debug such a Fiber issue?

[davidrapacchiale]

Closing this issue as it is related to an old version of the software. Either not relevant any longer, or fixed elsewhere. Please do reopen if still relevant.