Java runtime errors on launch: namespace reporting not enabled

I'm getting a couple errors on launch of Fiji that seem to be keeping me from being able to update the updatesites list, too.

I'm using a Macbook Pro (mid 2014) running Mojave 10.14.6
ImageJ version is 2.0.0-rc-69/1.52u (same errors appeared on 1.52p)
Build 269a0ad53f

Java is Version 8 Update 221 (build 1.8.0_221-b11) and my Java control panel claims that my system has the recommended version of Java.

The error message I get is below in the code tags, and when I google it, it appears that the error isn't something I can fix by changing settings at my end.

[ERROR] Error processing available update sites from ImageJ wiki
java.lang.RuntimeException: XPathFactory#newInstance() failed to create an XPathFactory for the default object model: http://java.sun.com/jaxp/xpath/dom with the XPathFactoryConfigurationException: javax.xml.xpath.XPathFactoryConfigurationException: java.util.ServiceConfigurationError: javax.xml.xpath.XPathFactory: jar:file:/Library/Java/Extensions/saxon9he.jar!/META-INF/services/javax.xml.xpath.XPathFactory:2: Illegal configuration-file syntax
	at javax.xml.xpath.XPathFactory.newInstance(XPathFactory.java:102)
	at org.scijava.util.XML.<init>(XML.java:142)
	at org.scijava.util.XML.<init>(XML.java:103)
	at net.imagej.util.MediaWikiClient.request(MediaWikiClient.java:234)
	at net.imagej.util.MediaWikiClient.query(MediaWikiClient.java:243)
	at net.imagej.util.MediaWikiClient.getPageSource(MediaWikiClient.java:109)
	at net.imagej.updater.util.AvailableSites.getAvailableSites(AvailableSites.java:79)
	at net.imagej.updater.util.AvailableSites.tryGetAvailableSites(AvailableSites.java:177)
	at net.imagej.updater.util.AvailableSites.initializeAndAddSites(AvailableSites.java:140)
	at net.imagej.ui.swing.updater.ImageJUpdater.refreshUpdateSites(ImageJUpdater.java:257)
	at net.imagej.ui.swing.updater.ImageJUpdater.run(ImageJUpdater.java:145)
	at org.scijava.command.CommandModule.run(CommandModule.java:199)
	at org.scijava.module.ModuleRunner.run(ModuleRunner.java:168)
	at org.scijava.module.ModuleRunner.call(ModuleRunner.java:127)
	at org.scijava.module.ModuleRunner.call(ModuleRunner.java:66)
	at org.scijava.thread.DefaultThreadService.lambda$wrap$2(DefaultThreadService.java:228)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
org.xml.sax.SAXException: Parser configuration problem: namespace reporting is not enabled
	at net.sf.saxon.event.ReceivingContentHandler.getNodeName(ReceivingContentHandler.java:383)
	at net.sf.saxon.event.ReceivingContentHandler.startElement(ReceivingContentHandler.java:291)
	at net.imagej.updater.XMLFileWriter.write(XMLFileWriter.java:156)
	at net.imagej.updater.FilesCollection.write(FilesCollection.java:439)
	at net.imagej.updater.util.AvailableSites.applySitesURLUpdates(AvailableSites.java:299)
	at net.imagej.ui.swing.updater.ImageJUpdater.refreshUpdateSites(ImageJUpdater.java:262)
	at net.imagej.ui.swing.updater.ImageJUpdater.run(ImageJUpdater.java:145)
	at org.scijava.command.CommandModule.run(CommandModule.java:199)
	at org.scijava.module.ModuleRunner.run(ModuleRunner.java:168)
	at org.scijava.module.ModuleRunner.call(ModuleRunner.java:127)
	at org.scijava.module.ModuleRunner.call(ModuleRunner.java:66)
	at org.scijava.thread.DefaultThreadService.lambda$wrap$2(DefaultThreadService.java:228)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)

Start with the stack-trace entry points in org.scijava.util.XML, net.imagej.util.MediaWikiClient, AvailableSites, and XMLFileWriter, then reproduce launch and update-site refresh on the reported Java and macOS setup. Trace the XPathFactory and namespace-reporting failures; done means Fiji launches and refreshes the update-sites list without either error.