"Log4j Visualizer" feature stopped working

For several months, the “Log4j Visualizer” feature stopped working on our Nexus OSS instance (currently in v3.42).
The ‘Statistics - recalculate vulnerabilities statistics’ automated task systematically returns the error below.
Do you have an idea about the origin of this problem and do you know how to fix it, please?

2022-11-15 00:04:00,894+0100 WARN [quartz-11-thread-18] *SYSTEM org.sonatype.nexus.quartz.internal.task.QuartzTaskJob - Task 62ea4d2c-22fe-4c16-96aa-973214473ed2 : ‘Statistics - recalculate vulnerabilities statistics’ [repository.vulnerability.statistics] execution failure
java.lang.NullPointerException: null
at java.util.regex.Matcher.getTextLength(Matcher.java:1283)
at java.util.regex.Matcher.reset(Matcher.java:309)
at java.util.regex.Matcher.(Matcher.java:229)
at java.util.regex.Pattern.matcher(Pattern.java:1093)
at com.sonatype.nexus.vulnerability.internal.log.RequestLogAggregator.extractDate(RequestLogAggregator.java:116)
at com.sonatype.nexus.vulnerability.internal.log.RequestLogAggregator.parseLogFiles(RequestLogAggregator.java:98)
at com.sonatype.nexus.vulnerability.internal.log.RequestLogAggregator.versionRequestCount(RequestLogAggregator.java:71)
at com.sonatype.nexus.vulnerability.internal.log.VulnerabilityRadarService.recalculateStatistics(VulnerabilityRadarService.java:68)
at com.sonatype.nexus.vulnerability.internal.log.VulnerabilityStatisticsTask.execute(VulnerabilityStatisticsTask.java:37)
at org.sonatype.nexus.scheduling.TaskSupport.call(TaskSupport.java:100)
at org.sonatype.nexus.quartz.internal.task.QuartzTaskJob.doExecute(QuartzTaskJob.java:143)
at org.sonatype.nexus.quartz.internal.task.QuartzTaskJob.execute(QuartzTaskJob.java:106)
at org.quartz.core.JobRunShell.run(JobRunShell.java:202)
at org.sonatype.nexus.quartz.internal.QuartzThreadPool.lambda$0(QuartzThreadPool.java:145)
at org.sonatype.nexus.thread.internal.MDCAwareRunnable.run(MDCAwareRunnable.java:40)
at org.apache.shiro.subject.support.SubjectRunnable.doRun(SubjectRunnable.java:120)
at org.apache.shiro.subject.support.SubjectRunnable.run(SubjectRunnable.java:108)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:750)

The log4j visualizer is powered by scanning the log files. It would appear that your request.log file has something we didn’t expect and is causing a null pointer exception. If you have a license you should contact support. Otherwise, could you open a bug in https://issues.sonatype.org against the NEXUS project and attach a support zip so we can look at the log file when attempting to diagnose this issue? You could probably work around the issue by clearing out your request.log files from /nexus3/log.

After clearing the older request.log files, the ‘Statistics - recalculate vulnerabilities statistics’ task runs correctly again. Thanks for your help.