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https://issues.apache.org/jira/browse/WICKET-6971?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17522822#comment-17522822
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ASF subversion and git services commented on WICKET-6971:
---------------------------------------------------------
Commit 541615be7d6fec61db84e6f1f94fc65227d22eef in wicket's branch
refs/heads/master from Ryo
[ https://gitbox.apache.org/repos/asf?p=wicket.git;h=541615be7d ]
[WICKET-6971] NullPointerException in ModificationWatcher (#510)
> NullPointerException in ModificationWatcher
> -------------------------------------------
>
> Key: WICKET-6971
> URL: https://issues.apache.org/jira/browse/WICKET-6971
> Project: Wicket
> Issue Type: Bug
> Environment: * Eclipse Version: 2021-12 (4.22.0) Build id:
> 20211202-1639
> * Tomcat 9.0.44
> * Java11(amazon-corretto-11.0.10.9.1-windows-x64-jdk)
> Reporter: Ryo Tsunoda
> Priority: Minor
>
> Sometimes this exception occurs after I edit the CSS.
>
> ```
> 2022-04-09 19:28:48.252 | ERROR | [ModificationWatcher Task] |
> org.apache.wicket.util.thread.Task | Unhandled exception thrown by user code
> in task ModificationWatcher
> java.lang.NullPointerException: null
> at org.apache.wicket.util.io.Connections.close(Connections.java:133)
> ~[wicket-util-8.14.0.jar:8.14.0]
> at
> org.apache.wicket.core.util.resource.UrlResourceStream.updateContentLength(UrlResourceStream.java:247)
> ~[wicket-core-8.14.0.jar:8.14.0]
> at
> org.apache.wicket.core.util.resource.UrlResourceStream.lastModifiedTime(UrlResourceStream.java:224)
> ~[wicket-core-8.14.0.jar:8.14.0]
> at
> org.apache.wicket.markup.MarkupResourceStream.lastModifiedTime(MarkupResourceStream.java:148)
> ~[wicket-core-8.14.0.jar:8.14.0]
> at
> org.apache.wicket.util.watch.ModificationWatcher.checkModified(ModificationWatcher.java:157)
> ~[wicket-util-8.14.0.jar:8.14.0]
> at
> org.apache.wicket.util.watch.ModificationWatcher$1.run(ModificationWatcher.java:143)
> ~[wicket-util-8.14.0.jar:8.14.0]
> at org.apache.wicket.util.thread.Task$1.run(Task.java:116)
> [wicket-util-8.14.0.jar:8.14.0]
> at java.lang.Thread.run(Thread.java:829) [?:?]
> ```
>
> connection.getInputStream() returns null.
> Wicket can check null here.
> [https://github.com/apache/wicket/blob/wicket-8.x/wicket-util/src/main/java/org/apache/wicket/util/io/Connections.java#L133]
>
> Tomcat's CachedResourceURLConnection#getInputStream() sometimes returns a
> WebResource instance with no stream.
> [https://github.com/apache/tomcat/blob/9.0.x/java/org/apache/catalina/webresources/CachedResource.java#L516]
>
> I don't know the conditions under which it can be reproduced.
>
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