[WICKET-6639] PageStoreManager$SessionEntry.clear produces NullPointerException

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 8.3.0
• Fix Version/s: 9.0.0-M1, 8.4.0, 7.14.0
• Component/s: wicket
• Assignee: Martin Tzvetanov Grigorov
• Reporter: Mikhail Fursov
• Created: 28/Feb/19 19:36
• Updated: 24/Apr/19 17:37
• Resolved: 02/Mar/19 21:51

Description

Sometimes when I return to my website after some period I see the following exception:

java.lang.NullPointerException
 at org.apache.wicket.page.PageStoreManager$SessionEntry.clear(PageStoreManager.java:365)
 at org.apache.wicket.page.PageStoreManager$SessionEntry.valueUnbound(PageStoreManager.java:353)
 at org.apache.catalina.session.StandardSession.removeAttributeInternal(StandardSession.java:1784)
 at org.apache.catalina.session.StandardSession.expire(StandardSession.java:856)
 at org.apache.catalina.session.StandardSession.isValid(StandardSession.java:659)
 at org.apache.catalina.session.ManagerBase.processExpires(ManagerBase.java:573)
 at org.apache.catalina.session.ManagerBase.backgroundProcess(ManagerBase.java:558)
 at org.apache.catalina.core.StandardContext.backgroundProcess(StandardContext.java:5496)
 at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1351)
 at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1355)
 at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1355)
 at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.run(ContainerBase.java:1333)

 

This is very hard to investigate what is the reason for this bug from my side because I do not have a stable reproducer , but I believe one of the following 1-line fixes in Wicket

1. Adding a null check for sessionCache before using it
2. Making sessionCache field never null

can resolve this problem.