When the version of the Eclipse checkstyle plugin below is installed, the ONAP checkstyle rules cause errors in the Eclipse log file.
Eclipse Checkstyle Plug-in 8.26.0.201911121319 net.sf.eclipsecs.feature.group Eclipse Checkstyle Plugin Development Team

When you upgrade the version of the Eclipse checkstyle plugion to version 8.26, you will notice an error in Eclipse for every project using the ONAP checkstyle profile.
"Checkstyle execution failed due to an internal error. Please check the error log for details"

The ONAP checkstyle file has two issues:
1) The LineLength modue is nested in the TreeWalker module
2) The JavadocMethod module has an illegal property called minLineCount

Check you Eclipse log in .metadata/.log, you will see the two following exceptions:

ENTRY net.sf.eclipsecs.core 4 0 2019-12-03 13:02:29.258
!MESSAGE Checkstyle-Plugin: cannot initialize module TreeWalker - TreeWalker is not allowed as a parent of LineLength Please review 'Parent Module' section for this Check in web documentation if Check is standard.
!STACK 0
com.puppycrawl.tools.checkstyle.api.CheckstyleException: cannot initialize module TreeWalker - TreeWalker is not allowed as a parent of LineLength Please review 'Parent Module' section for this Check in web documentation if Check is standard.
at com.puppycrawl.tools.checkstyle.Checker.setupChild(Checker.java:472)
at com.puppycrawl.tools.checkstyle.api.AutomaticBean.configure(AutomaticBean.java:198)
at net.sf.eclipsecs.core.builder.CheckerFactory.createCheckerInternal(CheckerFactory.java:255)
at net.sf.eclipsecs.core.builder.CheckerFactory.createChecker(CheckerFactory.java:127)
at net.sf.eclipsecs.core.builder.Auditor.runAudit(Auditor.java:140)
at net.sf.eclipsecs.core.builder.CheckstyleBuilder.handleBuildSelection(CheckstyleBuilder.java:307)
at net.sf.eclipsecs.core.builder.CheckstyleBuilder.build(CheckstyleBuilder.java:173)
at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:833)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:45)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:220)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:263)
at org.eclipse.core.internal.events.BuildManager$1.run(BuildManager.java:316)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:45)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:319)
at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:371)
at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:392)
at org.eclipse.core.internal.events.AutoBuildJob.doBuild(AutoBuildJob.java:154)
at org.eclipse.core.internal.events.AutoBuildJob.run(AutoBuildJob.java:244)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:63)
Caused by: com.puppycrawl.tools.checkstyle.api.CheckstyleException: TreeWalker is not allowed as a parent of LineLength Please review 'Parent Module' section for this Check in web documentation if Check is standard.
at com.puppycrawl.tools.checkstyle.TreeWalker.setupChild(TreeWalker.java:147)
at com.puppycrawl.tools.checkstyle.api.AutomaticBean.configure(AutomaticBean.java:198)
at com.puppycrawl.tools.checkstyle.Checker.setupChild(Checker.java:467)
... 18 more

and:
!ENTRY net.sf.eclipsecs.core 4 0 2019-12-03 12:56:31.421
!MESSAGE Checkstyle-Plugin: cannot initialize module TreeWalker - cannot initialize module JavadocMethod - Property 'minLineCount' does not exist, please check the documentation
!STACK 0
com.puppycrawl.tools.checkstyle.api.CheckstyleException: cannot initialize module TreeWalker - cannot initialize module JavadocMethod - Property 'minLineCount' does not exist, please check the documentation
at com.puppycrawl.tools.checkstyle.Checker.setupChild(Checker.java:472)
at com.puppycrawl.tools.checkstyle.api.AutomaticBean.configure(AutomaticBean.java:198)
at net.sf.eclipsecs.core.builder.CheckerFactory.createCheckerInternal(CheckerFactory.java:255)
at net.sf.eclipsecs.core.builder.CheckerFactory.createChecker(CheckerFactory.java:127)
at net.sf.eclipsecs.core.builder.Auditor.runAudit(Auditor.java:140)
at net.sf.eclipsecs.core.builder.CheckstyleBuilder.handleBuildSelection(CheckstyleBuilder.java:307)
at net.sf.eclipsecs.core.builder.CheckstyleBuilder.build(CheckstyleBuilder.java:173)
at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:833)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:45)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:220)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:263)
at org.eclipse.core.internal.events.BuildManager$1.run(BuildManager.java:316)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:45)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:319)
at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:371)
at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:392)
at org.eclipse.core.internal.events.AutoBuildJob.doBuild(AutoBuildJob.java:154)
at org.eclipse.core.internal.events.AutoBuildJob.run(AutoBuildJob.java:244)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:63)
Caused by: com.puppycrawl.tools.checkstyle.api.CheckstyleException: cannot initialize module JavadocMethod - Property 'minLineCount' does not exist, please check the documentation
at com.puppycrawl.tools.checkstyle.TreeWalker.setupChild(TreeWalker.java:135)
at com.puppycrawl.tools.checkstyle.api.AutomaticBean.configure(AutomaticBean.java:198)
at com.puppycrawl.tools.checkstyle.Checker.setupChild(Checker.java:467)
... 18 more
Caused by: com.puppycrawl.tools.checkstyle.api.CheckstyleException: Property 'minLineCount' does not exist, please check the documentation
at com.puppycrawl.tools.checkstyle.api.AutomaticBean.tryCopyProperty(AutomaticBean.java:223)
at com.puppycrawl.tools.checkstyle.api.AutomaticBean.configure(AutomaticBean.java:191)
at com.puppycrawl.tools.checkstyle.TreeWalker.setupChild(TreeWalker.java:130)
... 20 more