Reported here:
https://mail.openjdk.java.net/pipermail/kulla-dev/2020-June/002523.html

JShell crashes when typing a text block:
$ jshell
| Welcome to JShell -- Version 15-internal
| For an introduction type: /help intro

jshell> """
Exception in thread "main" java.lang.IllegalArgumentException
        at jdk.compiler/com.sun.tools.javac.util.JCDiagnostic.<init>(JCDiagnostic.java:600)
        at jdk.compiler/com.sun.tools.javac.util.JCDiagnostic$Factory.create(JCDiagnostic.java:283)
        at jdk.compiler/com.sun.tools.javac.util.JCDiagnostic$Factory.error(JCDiagnostic.java:111)
        at jdk.compiler/com.sun.tools.javac.util.AbstractLog.error(AbstractLog.java:145)
        at jdk.compiler/com.sun.tools.javac.parser.JavaTokenizer.lexError(JavaTokenizer.java:163)
        at jdk.compiler/com.sun.tools.javac.parser.JavaTokenizer.scanString(JavaTokenizer.java:449)
        at jdk.compiler/com.sun.tools.javac.parser.JavaTokenizer.readToken(JavaTokenizer.java:936)
        at jdk.compiler/com.sun.tools.javac.parser.Scanner.nextToken(Scanner.java:115)
        at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext.countPendingOpenBraces(ConsoleIOContext.java:988)
        at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext.lambda$new$3(ConsoleIOContext.java:182)
        at jdk.internal.le/jdk.internal.org.jline.reader.impl.LineReaderImpl.acceptLine(LineReaderImpl.java:2983)
        at jdk.internal.le/jdk.internal.org.jline.reader.impl.LineReaderImpl$1.apply(LineReaderImpl.java:3797)
        at jdk.internal.le/jdk.internal.org.jline.reader.impl.LineReaderImpl.readLine(LineReaderImpl.java:665)
        at jdk.internal.le/jdk.internal.org.jline.reader.impl.LineReaderImpl.readLine(LineReaderImpl.java:454)
        at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext.readLine(ConsoleIOContext.java:229)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool.getInput(JShellTool.java:1254)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool.run(JShellTool.java:1190)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool.start(JShellTool.java:991)
        at jdk.jshell/jdk.internal.jshell.tool.JShellToolBuilder.start(JShellToolBuilder.java:254)
        at jdk.jshell/jdk.internal.jshell.tool.JShellToolProvider.main(JShellToolProvider.java:120)