javadoc throws NPE with --ignore-source-errors option

ADDITIONAL SYSTEM INFORMATION :
$ java -version
openjdk version "11.0.11" 2021-04-20
OpenJDK Runtime Environment (build 11.0.11+9-Ubuntu-0ubuntu2.20.04)
OpenJDK 64-Bit Server VM (build 11.0.11+9-Ubuntu-0ubuntu2.20.04, mixed mode, sharing)

A DESCRIPTION OF THE PROBLEM :
Generating javadoc for a class using generics and extending another class, the process fails when the other class is not available. This worked previously with JDK 8, but fails with JDK 11 and 16.

REGRESSION : Last worked in version 8u291

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Create a source file with the contents specified in "Source code for an executable test case"
2. ${JAVA_HOME}/bin/javadoc Test.java
3. ${JAVA_HOME}/bin/javadoc --ignore-source-errors Test.java

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The HTML files are generated.
ACTUAL -
Without "--ignore-source-errors", the process exits with an error.

When adding "--ignore-source-errors", there is an exception:

Generating ./package-summary.html...
Generating ./package-tree.html...
javadoc: error - An internal exception has occurred.
(java.lang.NullPointerException)
Please file a bug against the javadoc tool via the Java bug reporting page
(http://bugreport.java.com) after checking the Bug Database (http://bugs.java.com)
for duplicates. Include error messages and the following diagnostic in your report. Thank you.
java.lang.NullPointerException
at jdk.compiler/com.sun.tools.javac.code.Types.erasure(Types.java:2340)
at jdk.compiler/com.sun.tools.javac.code.Types$14.visitTypeVar(Types.java:2398)
at jdk.compiler/com.sun.tools.javac.code.Types$14.visitTypeVar(Types.java:2348)
at jdk.compiler/com.sun.tools.javac.code.Type$TypeVar.accept(Type.java:1659)
at jdk.compiler/com.sun.tools.javac.code.Types$DefaultTypeVisitor.visit(Types.java:4857)
at jdk.compiler/com.sun.tools.javac.code.Types.erasure(Types.java:2343)
at jdk.compiler/com.sun.tools.javac.code.Types.erasure(Types.java:2329)
at jdk.compiler/com.sun.tools.javac.model.JavacTypes.erasure(JavacTypes.java:134)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.Utils$5.visitTypeVariable(Utils.java:1069)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.Utils$5.visitTypeVariable(Utils.java:1048)
at jdk.compiler/com.sun.tools.javac.code.Type$TypeVar.accept(Type.java:1695)
at java.compiler@11.0.11/javax.lang.model.util.AbstractTypeVisitor6.visit(AbstractTypeVisitor6.java:104)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.Utils.asTypeElement(Utils.java:1086)
at jdk.javadoc/jdk.javadoc.internal.doclets.formats.html.LinkInfoImpl.setContext(LinkInfoImpl.java:410)
at jdk.javadoc/jdk.javadoc.internal.doclets.formats.html.LinkInfoImpl.<init>(LinkInfoImpl.java:285)
at jdk.javadoc/jdk.javadoc.internal.doclets.formats.html.LinkFactoryImpl.getTypeParameterLink(LinkFactoryImpl.java:184)
at jdk.javadoc/jdk.javadoc.internal.doclets.formats.html.LinkFactoryImpl.getTypeParameterLinks(LinkFactoryImpl.java:167)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.links.LinkFactory.getLink(LinkFactory.java:196)
at jdk.javadoc/jdk.javadoc.internal.doclets.formats.html.HtmlDocletWriter.getLink(HtmlDocletWriter.java:679)
at jdk.javadoc/jdk.javadoc.internal.doclets.formats.html.HtmlDocletWriter.addPreQualifiedClassLink(HtmlDocletWriter.java:814)
at jdk.javadoc/jdk.javadoc.internal.doclets.formats.html.HtmlDocletWriter.addPreQualifiedStrongClassLink(HtmlDocletWriter.java:839)
at jdk.javadoc/jdk.javadoc.internal.doclets.formats.html.AbstractTreeWriter.addPartialInfo(AbstractTreeWriter.java:185)
at jdk.javadoc/jdk.javadoc.internal.doclets.formats.html.AbstractTreeWriter.addLevelInfo(AbstractTreeWriter.java:92)
at jdk.javadoc/jdk.javadoc.internal.doclets.formats.html.AbstractTreeWriter.addLevelInfo(AbstractTreeWriter.java:94)
at jdk.javadoc/jdk.javadoc.internal.doclets.formats.html.AbstractTreeWriter.addTree(AbstractTreeWriter.java:129)
at jdk.javadoc/jdk.javadoc.internal.doclets.formats.html.AbstractTreeWriter.addTree(AbstractTreeWriter.java:112)
at jdk.javadoc/jdk.javadoc.internal.doclets.formats.html.PackageTreeWriter.generatePackageTreeFile(PackageTreeWriter.java:115)
at jdk.javadoc/jdk.javadoc.internal.doclets.formats.html.PackageTreeWriter.generate(PackageTreeWriter.java:92)
at jdk.javadoc/jdk.javadoc.internal.doclets.formats.html.HtmlDoclet.generatePackageFiles(HtmlDoclet.java:312)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.AbstractDoclet.startGeneration(AbstractDoclet.java:210)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.AbstractDoclet.run(AbstractDoclet.java:114)
at jdk.javadoc/jdk.javadoc.doclet.StandardDoclet.run(StandardDoclet.java:72)
at jdk.javadoc/jdk.javadoc.internal.tool.Start.parseAndExecute(Start.java:588)
at jdk.javadoc/jdk.javadoc.internal.tool.Start.begin(Start.java:432)
at jdk.javadoc/jdk.javadoc.internal.tool.Start.begin(Start.java:345)
at jdk.javadoc/jdk.javadoc.internal.tool.Main.execute(Main.java:63)
at jdk.javadoc/jdk.javadoc.internal.tool.Main.main(Main.java:52)

---------- BEGIN SOURCE ----------
import invalid.example.OtherClass;

public class Test<T> extends OtherClass<T> {

}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Use JDK 8 to build the javadoc.

FREQUENCY : always