Error while loading DOCTYPE subset : java.lang.NullPointerException

[angelozerr]

Given this XML file:

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE root-element SYSTEM "foo.dtd">
<root-element>
  &|
</root-element>

Open the completion and you see the error log

[Error - 17:51:00] May 28, 2020 05:51:00 org.eclipse.lemminx.extensions.dtd.contentmodel.CMDTDContentModelProvider createInternalCMDocument()
Message: Error while loading DOCTYPE subset
java.lang.NullPointerException
	at org.eclipse.lemminx.extensions.dtd.contentmodel.CMDTDDocument.loadInternalDTD(CMDTDDocument.java:357)
	at org.eclipse.lemminx.extensions.dtd.contentmodel.CMDTDContentModelProvider.createInternalCMDocument(CMDTDContentModelProvider.java:94)
	at org.eclipse.lemminx.extensions.contentmodel.model.ContentModelManager.findCMDocument(ContentModelManager.java:109)
	at org.eclipse.lemminx.extensions.contentmodel.model.ContentModelManager.findCMDocument(ContentModelManager.java:94)
	at org.eclipse.lemminx.extensions.contentmodel.model.ContentModelManager.findCMDocument(ContentModelManager.java:77)
	at org.eclipse.lemminx.extensions.contentmodel.participants.ContentModelCompletionParticipant.onXMLContent(ContentModelCompletionParticipant.java:363)
	at org.eclipse.lemminx.services.XMLCompletions.collectInsideContent(XMLCompletions.java:739)
	at org.eclipse.lemminx.services.XMLCompletions.doComplete(XMLCompletions.java:224)
	at org.eclipse.lemminx.services.XMLLanguageService.doComplete(XMLLanguageService.java:139)
	at org.eclipse.lemminx.XMLTextDocumentService.lambda$completion$1(XMLTextDocumentService.java:189)
	at java.base/java.util.concurrent.CompletableFuture.biApply(CompletableFuture.java:1236)
	at java.base/java.util.concurrent.CompletableFuture$BiApply.tryFire(CompletableFuture.java:1205)
	at java.base/java.util.concurrent.CompletableFuture$Completion.exec(CompletableFuture.java:479)
	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)
	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1020)
	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)
	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)
	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:177)