[SCXML-180] Prevent NPEs for possible null value returned from Evaluator.eval* methods

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.0
• Fix Version/s: 2.0
• Assignee: Woonsan Ko
• Reporter: Ate Douma
• Created: 03/Dec/13 13:29
• Updated: 04/Dec/13 14:39
• Resolved: 04/Dec/13 14:39

Description

I just encountered the following NPE:

java.lang.NullPointerException
at org.apache.commons.scxml2.semantics.SCXMLSemanticsImpl.filterTransitionsSet(SCXMLSemanticsImpl.java:415)
at org.apache.commons.scxml2.SCXMLExecutor.triggerEvents(SCXMLExecutor.java:124)
at org.apache.commons.scxml2.SCXMLExecutor.reset(SCXMLExecutor.java:256)
at org.apache.commons.scxml2.SCXMLExecutor.go(SCXMLExecutor.java:349)

This turned out to be caused by an transition condition (evaluated through Jexl) resulting in, and thus also returning, a null value.
A quick scan through the usages of Evaluator.eval* method shows several locations within SCXML where it always assumes an non-null value (Boolean or otherwise) to be returned. All possible sources for unexpected NPEs.

I think that for at least the Evaluator#evalCond method, which is assumed to return a Boolean, either an error should be catched/returned or maybe even assume null == Boolean.FALSE.

Issue Links

• is related to: SCXML-182 Support error event raising to comply the spec "3.12.2 Errors"