Corda: Adding muliple output states in a single transaction - kotlin

Question

In our use case we have to add two output states with different contracts to a transaction. I tried to add multiple states to transaction in withItems. I call this flow from an RPC but it throws an exception as java.lang.IllegalArgumentException: List has more than one element. while signing the transaction.
This is how I am adding multiple output states:-
val outputstate1 = IouState1(dataModel1, me, otherParty)
val outputstate2 = IouState2(dataModel2, me, otherParty)
val cmd1 = Command(IouContract1.Commands.Create(), state1.participants.map { it.owningKey })
val cmd2 = Command(IouContract2.Commands.Initiated(), state2.participants.map { it.owningKey })
val txBuilder = TransactionBuilder(TransactionType.General, notary).withItems(state1, state2, cmd1, cmd2)
progressTracker.currentStep = VERIFYING_TRANSACTION
// Verifying the transaction.
txBuilder.toWireTransaction().toLedgerTransaction(serviceHub).verify()
progressTracker.currentStep = SIGNING_TRANSACTION
// Signing the transaction.
val partSignedTx = serviceHub.signInitialTransaction(txBuilder)
progressTracker.currentStep = GATHERING_SIGS
// Send the state to the counterparty, and receive it back with their signature.
val fullySignedTx = subFlow(CollectSignaturesFlow(partSignedTx, GATHERING_SIGS.childProgressTracker()))
// Finalising the transaction.
progressTracker.currentStep = FINALISING_TRANSACTION
// Notarise and record the transaction in both parties' vaults.
return subFlow(FinalityFlow(fullySignedTx, FINALISING_TRANSACTION.childProgressTracker())).single()
Stack trace:-
net.corda.core.flows.FlowException: java.lang.IllegalArgumentException: List has more than one element.
at net.corda.core.flows.SignTransactionFlow.call(CollectSignaturesFlow.kt:202) ~[corda-core-0.14.0.jar:?]
at net.corda.core.flows.SignTransactionFlow.call(CollectSignaturesFlow.kt:175) ~[corda-core-0.14.0.jar:?]
at net.corda.core.flows.FlowLogic.subFlow(FlowLogic.kt:166) ~[corda-core-0.14.0.jar:?]
at com.dwlabcorda.salescontract.LOCReceiverFlow.call(LOCContractFlow.kt:107) ~[tradefinancecorda-0.1.jar:?]
at com.dwlabcorda.salescontract.LOCReceiverFlow.call(LOCContractFlow.kt:95) ~[tradefinancecorda-0.1.jar:?]
at net.corda.node.services.statemachine.FlowStateMachineImpl.run(FlowStateMachineImpl.kt:101) [corda-node-0.14.0.jar:?]
at net.corda.node.services.statemachine.FlowStateMachineImpl.run(FlowStateMachineImpl.kt:33) [corda-node-0.14.0.jar:?]
at co.paralleluniverse.fibers.Fiber.run1(Fiber.java:1067) [quasar-core-0.7.6-jdk8.jar:0.7.6]
at co.paralleluniverse.fibers.Fiber.exec(Fiber.java:767) [quasar-core-0.7.6-jdk8.jar:0.7.6]
at co.paralleluniverse.fibers.RunnableFiberTask.doExec(RunnableFiberTask.java:100) [quasar-core-0.7.6-jdk8.jar:0.7.6]
at co.paralleluniverse.fibers.RunnableFiberTask.run(RunnableFiberTask.java:91) [quasar-core-0.7.6-jdk8.jar:0.7.6]
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) [?:1.8.0_144]
at java.util.concurrent.FutureTask.run(Unknown Source) [?:1.8.0_144]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(Unknown Source) [?:1.8.0_144]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source) [?:1.8.0_144]
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [?:1.8.0_144]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [?:1.8.0_144]
at net.corda.node.utilities.AffinityExecutor$ServiceAffinityExecutor$1$thread$1.run(AffinityExecutor.kt:69) [corda-node-0.14.0.jar:?]
Caused by: java.lang.IllegalArgumentException: List has more than one element.
at kotlin.collections.CollectionsKt___CollectionsKt.single(_Collections.kt:471) ~[kotlin-stdlib-1.1.1.jar:1.1.1]
at com.dwlabcorda.salescontract.LOCReceiverFlow$call$signTransactionFlow$1.checkTransaction(LOCContractFlow.kt:100) ~[tradefinancecorda-0.1.jar:?]
at net.corda.core.flows.SignTransactionFlow.call(CollectSignaturesFlow.kt:199) ~[corda-core-0.14.0.jar:?]
... 17 more

Answer 1

Probably you used a .single() cast in one of your contracts that is now throwing an exception