The following exception occurred when playing with a very simple test case across different JDK versions. Although the error is "deep" in javac, it only occurs when javac is invoked via javadoc. The error does not appear for any recent version of JDK javac.

The issue first shows up in JDK 13 (9 through 12 are OK) and so counts as a regression.

Attached is the original test case. Here is the output from the test, showing the exceptions:
$ sh play/extract/run.sh 2>&1 | tee play/extract/log
Compiling with 9
Documenting with 9
Creating destination directory: "play/extract/api-9/"
Compiling with 10
Documenting with 10
Creating destination directory: "play/extract/api-10/"
javadoc: warning - You have not specified the version of HTML to use.
The default is currently HTML 4.01, but this will change to HTML5
in a future release. To suppress this warning, please specify the
version of HTML used in your documentation comments and to be
generated by this doclet, using the -html4 or -html5 options.
1 warning
Compiling with 11
Documenting with 11
Creating destination directory: "play/extract/api-11/"
Compiling with 12
Documenting with 12
Creating destination directory: "play/extract/api-12/"
Compiling with 13
Documenting with 13
javadoc: error - fatal error encountered: java.lang.AssertionError
javadoc: error - 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.AssertionError
at jdk.compiler/com.sun.tools.javac.util.Assert.error(Assert.java:155)
at jdk.compiler/com.sun.tools.javac.util.Assert.check(Assert.java:46)
at jdk.compiler/com.sun.tools.javac.comp.Annotate.lambda$annotateLater$0(Annotate.java:252)
at jdk.compiler/com.sun.tools.javac.comp.Annotate.flush(Annotate.java:191)
at jdk.compiler/com.sun.tools.javac.comp.Annotate.unblockAnnotations(Annotate.java:144)
at jdk.compiler/com.sun.tools.javac.comp.Annotate.enterDone(Annotate.java:157)
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.enterDone(JavaCompiler.java:1746)
at jdk.javadoc/jdk.javadoc.internal.tool.JavadocEnter.main(JavadocEnter.java:80)
at jdk.javadoc/jdk.javadoc.internal.tool.JavadocTool.getEnvironment(JavadocTool.java:212)
at jdk.javadoc/jdk.javadoc.internal.tool.Start.parseAndExecute(Start.java:543)
at jdk.javadoc/jdk.javadoc.internal.tool.Start.begin(Start.java:399)
at jdk.javadoc/jdk.javadoc.internal.tool.Start.begin(Start.java:345)
at jdk.javadoc/jdk.javadoc.internal.tool.Main.execute(Main.java:63)
at jdk.javadoc/jdk.javadoc.internal.tool.Main.main(Main.java:52)
2 errors
find: ‘play/extract/api-13’: No such file or directory
Compiling with 14
Documenting with 14
javadoc: error - fatal error encountered: java.lang.AssertionError
javadoc: error - Please file a bug against the javadoc tool via the Java bug reporting page
(http://bugreport.java.com) after checking the Bug Database (http://bugs.java.com)
for duplicates. Include error messages and the following diagnostic in your report. Thank you.
java.lang.AssertionError
at jdk.compiler/com.sun.tools.javac.util.Assert.error(Assert.java:155)
at jdk.compiler/com.sun.tools.javac.util.Assert.check(Assert.java:46)
at jdk.compiler/com.sun.tools.javac.comp.Annotate.lambda$annotateLater$0(Annotate.java:252)
at jdk.compiler/com.sun.tools.javac.comp.Annotate.flush(Annotate.java:191)
at jdk.compiler/com.sun.tools.javac.comp.Annotate.unblockAnnotations(Annotate.java:144)
at jdk.compiler/com.sun.tools.javac.comp.Annotate.enterDone(Annotate.java:157)
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.enterDone(JavaCompiler.java:1752)
at jdk.javadoc/jdk.javadoc.internal.tool.JavadocEnter.main(JavadocEnter.java:78)
at jdk.javadoc/jdk.javadoc.internal.tool.JavadocTool.getEnvironment(JavadocTool.java:210)
at jdk.javadoc/jdk.javadoc.internal.tool.Start.parseAndExecute(Start.java:540)
at jdk.javadoc/jdk.javadoc.internal.tool.Start.begin(Start.java:396)
at jdk.javadoc/jdk.javadoc.internal.tool.Start.begin(Start.java:342)
at jdk.javadoc/jdk.javadoc.internal.tool.Main.execute(Main.java:63)
at jdk.javadoc/jdk.javadoc.internal.tool.Main.main(Main.java:52)
2 errors
find: ‘play/extract/api-14’: No such file or directory
Compiling with jdk.ref
Documenting with jdk.ref
javadoc: error - fatal error encountered: java.lang.AssertionError
javadoc: error - Please file a bug against the javadoc tool via the Java bug reporting page
(http://bugreport.java.com) after checking the Bug Database (http://bugs.java.com)
for duplicates. Include error messages and the following diagnostic in your report. Thank you.
java.lang.AssertionError
at jdk.compiler/com.sun.tools.javac.util.Assert.error(Assert.java:155)
at jdk.compiler/com.sun.tools.javac.util.Assert.check(Assert.java:46)
at jdk.compiler/com.sun.tools.javac.comp.Annotate.lambda$annotateLater$0(Annotate.java:252)
at jdk.compiler/com.sun.tools.javac.comp.Annotate.flush(Annotate.java:191)
at jdk.compiler/com.sun.tools.javac.comp.Annotate.unblockAnnotations(Annotate.java:144)
at jdk.compiler/com.sun.tools.javac.comp.Annotate.enterDone(Annotate.java:157)
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.enterDone(JavaCompiler.java:1752)
at jdk.javadoc/jdk.javadoc.internal.tool.JavadocEnter.main(JavadocEnter.java:78)
at jdk.javadoc/jdk.javadoc.internal.tool.JavadocTool.getEnvironment(JavadocTool.java:209)
at jdk.javadoc/jdk.javadoc.internal.tool.Start.parseAndExecute(Start.java:536)
at jdk.javadoc/jdk.javadoc.internal.tool.Start.begin(Start.java:396)
at jdk.javadoc/jdk.javadoc.internal.tool.Start.begin(Start.java:342)
at jdk.javadoc/jdk.javadoc.internal.tool.Main.execute(Main.java:63)
at jdk.javadoc/jdk.javadoc.internal.tool.Main.main(Main.java:52)
2 errors
find: ‘play/extract/api-jdk.ref’: No such file or directory