Fails to show VisualGC for ZGC

Describe the bug
When running a large java app using the ZGC garbage collector, the VisualVM tab VisualGC falsely claims it doesn't support the running JVM (whereas actually, it's the chosen GC that represents a problem).

To Reproduce
Steps to reproduce the behavior:
1 Start VisualVM
2 Start a JVM app using the commandline option -XX+UseZGC
3 Find the newly started app in VisualVM and click the VisualGC tab
4 See error

Expected behavior
A very nice graphical representation of the current state of the memory use should be displayed

VisualVM log
INFO [com.sun.jvmstat.tools.visualgc.VisualGCView]: Could not create GCSample
java.lang.NullPointerException: Cannot invoke "sun.jvmstat.monitor.LongMonitor.longValue()" because "this.edenSize" is null
at com.sun.jvmstat.tools.visualgc.MonitoredVmModel.getNewGenMaxSize(MonitoredVmModel.java:250)
at com.sun.jvmstat.tools.visualgc.GCSample.(GCSample.java:131)
[catch] at com.sun.jvmstat.tools.visualgc.VisualGCView.initializeModel(VisualGCView.java:218)
at com.sun.jvmstat.tools.visualgc.VisualGCView.(VisualGCView.java:103)
at org.graalvm.visualvm.modules.visualgc.VisualGCViewProvider.createView(VisualGCViewProvider.java:26)
at org.graalvm.visualvm.modules.visualgc.VisualGCViewProvider.createView(VisualGCViewProvider.java:19)
at org.graalvm.visualvm.core.ui.DataSourceViewProvider.getView(DataSourceViewProvider.java:103)
at org.graalvm.visualvm.core.ui.DataSourceViewsManager.getViews(DataSourceViewsManager.java:137)
at org.graalvm.visualvm.core.ui.DataSourceWindowManager.openWindowAndAddView(DataSourceWindowManager.java:263)
at org.graalvm.visualvm.core.ui.DataSourceWindowManager.access$000(DataSourceWindowManager.java:53)
at org.graalvm.visualvm.core.ui.DataSourceWindowManager$2.run(DataSourceWindowManager.java:122)
at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1418)
at org.netbeans.modules.openide.util.GlobalLookup.execute(GlobalLookup.java:45)
at org.openide.util.lookup.Lookups.executeWith(Lookups.java:278)
at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2033)

Desktop (please complete the following information):

• OS: Ubuntu 20.10 and Ubuntu 20.04
• JDK version JDK 15
• VisualVM version 2.0.5

Additional context
Very cold weather today

Start with MonitoredVmModel.java at getNewGenMaxSize, then read GCSample.java and VisualGCView.java around the reported stack trace. Reproduce with a Java 15 application using -XX+UseZGC and open VisualGC; done means the tab no longer falsely reports unsupported JVM behavior or fails with the shown NullPointerException.