Is the package https://directory.apache.org/studio/download/download-linux.html ? If so then this would seem to be an Eclipse product, so everything needed would be packaged. I don't think this depends on anything from the (Fedora) system other than a compatible version of Java, which you seem to have since you were able to start it up.

I tried going to Preferences -> Connections -> Certificate Validation but didn't see any, and no NPE was generated so I think the most appropriate place for this issue is probably somewhere in https://directory.apache.org/issue-tracking.html .

the way I installed it, I'd presume most of us do it since it the easiest, was as a "Plugins for Eclipse"

Ok, so I've tried both the Apache Directory Studio product as before, and taken Fedora Eclipse and installed from the update site mentioned in https://directory.apache.org/studio/installation-in-eclipse.html .

In both cases, this is the NPE I see when adding a certificate :

java.lang.NullPointerException
	at org.apache.directory.studio.connection.ui.widgets.CertificateListComposite$1.selectionChanged(CertificateListComposite.java:114)
	at org.eclipse.jface.viewers.Viewer$2.run(Viewer.java:163)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
	at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:50)
	at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:173)
	at org.eclipse.jface.viewers.Viewer.fireSelectionChanged(Viewer.java:160)
	at org.eclipse.jface.viewers.StructuredViewer.updateSelection(StructuredViewer.java:2197)
	at org.eclipse.jface.viewers.StructuredViewer.handleSelect(StructuredViewer.java:1228)
	at org.eclipse.jface.viewers.StructuredViewer$4.widgetSelected(StructuredViewer.java:1257)
	at org.eclipse.jface.util.OpenStrategy.fireSelectionEvent(OpenStrategy.java:242)
	at org.eclipse.jface.util.OpenStrategy.access$4(OpenStrategy.java:236)
	at org.eclipse.jface.util.OpenStrategy$1.handleEvent(OpenStrategy.java:408)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4493)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1329)
	at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3831)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3442)
	at org.eclipse.jface.window.Window.runEventLoop(Window.java:827)
	at org.eclipse.jface.window.Window.open(Window.java:803)
	at org.eclipse.ui.internal.dialogs.WorkbenchPreferenceDialog.open(WorkbenchPreferenceDialog.java:211)
	at org.eclipse.ui.internal.OpenPreferencesAction.run(OpenPreferencesAction.java:63)
	at org.eclipse.jface.action.Action.runWithEvent(Action.java:473)
	at org.eclipse.jface.action.ActionContributionItem.handleWidgetSelection(ActionContributionItem.java:595)
	at org.eclipse.jface.action.ActionContributionItem.access$2(ActionContributionItem.java:511)
	at org.eclipse.jface.action.ActionContributionItem$5.handleEvent(ActionContributionItem.java:420)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4493)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1329)
	at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3831)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3442)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$4.run(PartRenderingEngine.java:1127)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:337)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1018)
	at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:156)
	at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:654)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:337)
	at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:598)
	at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:150)
	at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:139)
	at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:380)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:235)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:669)
	at org.eclipse.equinox.launcher.Main.basicRun(Main.java:608)
	at org.eclipse.equinox.launcher.Main.run(Main.java:1515)
	at org.eclipse.equinox.launcher.Main.main(Main.java:1488)
	
The problem looks to originate in Apache Directory Studio code so it should probably be filed there.

I'm going to mark this as CLOSED(CANTFIX) because any existing bug would seem to be in the Apache Directory Studio code itself, and should be filed upstream.

yes, I did reported it upstream, had been thanked. Thanks.

yes, I did report it upstream, had been thanked. Thanks.