Sometimes, for some unknown reason, the report category version file is empty and NullPointerException will be thrown like below:

java.lang.NullPointerException
     at com.pmease.quickbuild.plugin.report.engine.migration.VersionFile.read(VersionFile.java:32)
     at com.pmease.quickbuild.plugin.report.engine.migration.MigrationExecutor.readDataVersion(MigrationExecutor.java:41)
     at com.pmease.quickbuild.plugin.report.engine.migration.MigrationExecutor.needUpgrade(MigrationExecutor.java:92)
     at com.pmease.quickbuild.plugin.report.engine.migration.MigrationExecutor.doUpgrade(MigrationExecutor.java:65)
     at com.pmease.quickbuild.plugin.report.engine.migration.MigrationExecutor.upgrade(MigrationExecutor.java:102)
     at com.pmease.quickbuild.plugin.report.engine.metadata.ReportCategory.upgrade(ReportCategory.java:801)
     at com.pmease.quickbuild.plugin.report.changes.ChangesCategory.getCategoryDirOfBuild(ChangesCategory.java:102)
     at com.pmease.quickbuild.plugin.report.engine.metadata.ReportCategory.getReportSetsOfBuild(ReportCategory.java:525)
     at com.pmease.quickbuild.plugin.report.changes.ChangesCategory.getReportSetsOfBuild(ChangesCategory.java:121)
     at com.pmease.quickbuild.plugin.report.engine.contribution.web.CategoryBuildTab.getTabs(CategoryBuildTab.java:66)
     at com.pmease.quickbuild.web.page.build.BuildPage.onInitialize(BuildPage.java:741)
     at org.apache.wicket.Component.fireInitialize(Component.java:924)
     at org.apache.wicket.MarkupContainer.internalInitialize(MarkupContainer.java:1002)
     at org.apache.wicket.Page.internalPrepareForRender(Page.java:278)
     at org.apache.wicket.Component.render(Component.java:2280)
     at org.apache.wicket.Page.renderPage(Page.java:1035)
     at org.apache.wicket.request.handler.render.WebPageRenderer.renderPage(WebPageRenderer.java:105)
     at org.apache.wicket.request.handler.render.WebPageRenderer.respond(WebPageRenderer.java:182)
     at org.apache.wicket.request.handler.RenderPageRequestHandler.respond(RenderPageRequestHandler.java:147)
     at org.apache.wicket.request.cycle.RequestCycle$HandlerExecutor.respond(RequestCycle.java:719)
     at org.apache.wicket.request.RequestHandlerStack.execute(RequestHandlerStack.java:63)