ledger transfers fail with non-specific exceptions on alpha

Given an account that holds tokens of a certain type, issued by different notaries, the transfer fails if there insufficient funds allocated to the notary that is being used for the transfer.

This is the stack trace:

java.util.NoSuchElementException: Collection is empty.
	at kotlin.collections.CollectionsKt___CollectionsKt.first(_Collections.kt:166) ~[kotlin-stdlib-1.1.60.jar:1.1.60-release-55 (1.1.60)]
	at io.cordite.dgl.corda.token.flows.TransferTokenSenderFunctions$Companion.computeOutputs(TransferTokenUtilities.kt:91) ~[dgl-cordapp-0.0.1.jar:?]
	at io.cordite.dgl.corda.token.flows.TransferTokenSenderFunctions$Companion.prepareTokenMove(TransferTokenUtilities.kt:58) ~[dgl-cordapp-0.0.1.jar:?]
	at io.cordite.dgl.corda.token.flows.TransferTokenFlow.call(TransferTokenFlow.kt:28) ~[dgl-cordapp-0.0.1.jar:?]
	at io.cordite.dgl.corda.token.flows.TransferTokenFlow.call(TransferTokenFlow.kt:17) ~[dgl-cordapp-0.0.1.jar:?]
	at net.corda.node.services.statemachine.FlowStateMachineImpl.run(FlowStateMachineImpl.kt:96) [corda-node-corda-3.0.jar:?]
	at net.corda.node.services.statemachine.FlowStateMachineImpl.run(FlowStateMachineImpl.kt:44) [corda-node-corda-3.0.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$RunnableAdapter.call(Executors.java:511) [?:1.8.0_163]
	at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_163]
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) [?:1.8.0_163]
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) [?:1.8.0_163]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_163]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_163]
	at net.corda.node.utilities.AffinityExecutor$ServiceAffinityExecutor$1$thread$1.run(AffinityExecutor.kt:62) [corda-node-corda-3.0.jar:?]

This needs to be resolved two-fold:

1. report something more meaningful than: java.util.NoSuchElementException: Collection is empty.
2. implement implicit notary transfers to keep the dgl api simple