Javascriptlet Operation HPOO 10.60

I recently converted a 9.07 flow which uses a custom javascriplet operation. I got no warnings or errors during the conversion or while importing the project. The javascriplet works well for the most. Occasionally it gets fed an input that causes the flow to halt "Failed to Complete"

in Studio, when I pass that input string in, the error is as follows

com.iconclude.dharma.runengine.RunException: Exception occurred during navigation calculation. Did not find Flow Exception Step id.
 at com.iconclude.dharma.runengine.view.BeanViewBuilder.updateRunView(BeanViewBuilder.java:524)
 at com.iconclude.dharma.runengine.view.DefaultRunViewFactory.updateView(DefaultRunViewFactory.java:61)
 at com.iconclude.dharma.runengine.debugger.RunControlImpl.onEvent(RunControlImpl.java:236)
 at com.hp.oo.studio.debugger.engine.AbstractDebugRunEventsChannel.notifyListeners(AbstractDebugRunEventsChannel.java:50)
 at com.hp.oo.studio.debugger.engine.AbstractDebugRunEventsChannel.processFinishEvent(AbstractDebugRunEventsChannel.java:102)
 at com.hp.oo.studio.debugger.events.StudioDebuggerEventsBuffer.processFinishEvent(StudioDebuggerEventsBuffer.java:98)
 at com.hp.oo.studio.debugger.engine.AbstractDebugRunEventsChannel.processEvent(AbstractDebugRunEventsChannel.java:83)
 at com.hp.oo.studio.debugger.events.StudioDebuggerEventsBuffer$DebuggerEventsConsumer.run(StudioDebuggerEventsBuffer.java:120)
Caused by: java.lang.Exception: Exception occurred during navigation calculation. Did not find Flow Exception Step id.
 ... 8 more

It seems in Studio 10, the javascript debugger is no longer present? When I use an IDE to test and debug the script, I get no errors. Still I know there are some nuance differences between the javascript used in HPOO and what you might find in an IDE. Any ideas how I find what is bugging HPOO about the scriplet?