Better error handling.
… org.jenkinsci.plugins.workflow.flow.FlowExecutionList$StepExecutionIteratorImpl$1 onSuccess
WARNING: null
java.lang.NumberFormatException: For input string: ""
	at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
	at java.lang.Integer.parseInt(Integer.java:504)
	at java.lang.Integer.parseInt(Integer.java:527)
	at org.jenkinsci.plugins.durabletask.FileMonitoringTask$FileMonitoringController.exitStatus(FileMonitoringTask.java:107)
	at org.jenkinsci.plugins.workflow.steps.durable_task.DurableTaskStep$Execution.check(DurableTaskStep.java:133)
	at org.jenkinsci.plugins.workflow.steps.durable_task.DurableTaskStep$Execution.access$100(DurableTaskStep.java:70)
	at org.jenkinsci.plugins.workflow.steps.durable_task.DurableTaskStep$Checker$1.apply(DurableTaskStep.java:161)
	at org.jenkinsci.plugins.workflow.steps.durable_task.DurableTaskStep$Checker$1.apply(DurableTaskStep.java:159)
	at …