It looks like upgrading to NB 8.2 will resolve this problem.
java.lang.UnsupportedOperationException: The InputOutput doesn't support folding
at org.openide.windows.IOFolding.startFold(IOFolding.java:143)
at org.netbeans.modules.maven.execute.cmd.ExecutionEventObject$Tree.startFold(ExecutionEventObject.java:205)
at org.netbeans.modules.maven.execute.CommandLineOutputHandler$Output.run(CommandLineOutputHandler.java:377)
at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1443)
at org.netbeans.modules.openide.util.GlobalLookup.execute(GlobalLookup.java:68)
at org.openide.util.lookup.Lookups.executeWith(Lookups.java:303)
[catch] at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2058)
It looks like upgrading to NB 8.2 will resolve this problem.