Error converting category to a transfer

[jonestimd]

Changing the category of an existing transaction detail to a transfer causes the following exception:

	at java.util.Objects.requireNonNull(Objects.java:228)
	at java.util.stream.Collectors.lambda$groupingBy$45(Collectors.java:907)
	at java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java:169)
	at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1382)
	at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
	at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
	at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
	at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
	at io.github.jonestimd.finance.domain.event.DomainEvent.index(DomainEvent.java:45)
	at io.github.jonestimd.finance.domain.event.DomainEvent.<init>(DomainEvent.java:64)
	at io.github.jonestimd.finance.domain.event.TransactionEvent.<init>(TransactionEvent.java:31)
	at io.github.jonestimd.finance.swing.transaction.action.CommitAction.removeStaleEntities(CommitAction.java:109)
	at io.github.jonestimd.finance.swing.transaction.action.CommitAction.updateUI(CommitAction.java:91)
	at io.github.jonestimd.finance.swing.transaction.action.CommitAction.updateUI(CommitAction.java:45)
	at io.github.jonestimd.swing.BackgroundTask$1.updateUI(BackgroundTask.java:122)
	at io.github.jonestimd.swing.BackgroundTask.lambda$run$0(BackgroundTask.java:161)
	at java.util.concurrent.CompletableFuture.uniWhenComplete(CompletableFuture.java:760)
	at java.util.concurrent.CompletableFuture$UniWhenComplete.tryFire(CompletableFuture.java:736)
	at java.util.concurrent.CompletableFuture$Completion.run(CompletableFuture.java:442)
	at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
	at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
	at java.awt.EventQueue.access$500(EventQueue.java:97)
	at java.awt.EventQueue$3.run(EventQueue.java:709)
	at java.awt.EventQueue$3.run(EventQueue.java:703)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)