If a slave is put offline during a running build, the timestamper plugin issues a NPE at the end of the build, marking the build as failed.

The stacktrace is the following

17:11:18 Looks like the node went offline during the build. Check the slave log for the details.FATAL: null
17:11:18 java.lang.NullPointerException
17:11:18 at hudson.plugins.timestamper.TimestampFormatter.<init>(TimestampFormatter.java:71)
17:11:20 at hudson.plugins.timestamper.TimestamperConfig$1.get(TimestamperConfig.java:59)
17:11:20 at hudson.plugins.timestamper.TimestamperConfig$1.get(TimestamperConfig.java:54)
17:11:20 at hudson.plugins.timestamper.TimestamperConfig.formatter(TimestamperConfig.java:148)
17:11:20 at hudson.plugins.timestamper.annotator.TimestampAnnotatorFactory.newInstance(TimestampAnnotatorFactory.java:51)
17:11:20 at hudson.console.ConsoleAnnotator._for(ConsoleAnnotator.java:143)
17:11:20 at hudson.console.ConsoleAnnotator.initial(ConsoleAnnotator.java:133)
17:11:20 at hudson.console.AnnotatedLargeText.createAnnotator(AnnotatedLargeText.java:138)
17:11:20 at hudson.console.AnnotatedLargeText.writeHtmlTo(AnnotatedLargeText.java:155)
17:11:20 at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:605)
17:11:20 at hudson.model.Run.execute(Run.java:1543)
17:11:20 at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
17:11:20 at hudson.model.ResourceController.execute(ResourceController.java:88)
17:11:20 at hudson.model.Executor.run(Executor.java:236)