It appears in some scenarios JShell can cause a `JCDiagnostic`s to be generated in a scenario where there is a source code position defined but no current source file defined, which explicitly disallowed by the `JCDiagnostic` constructor. As a result, an `IllegalArgumentException` is thrown.

Reproducer:

    $ jshell
    | Welcome to JShell -- Version 25-ea
    | For an introduction type: /help intro
    
    jshell> import jdk.jshell.*
    
    jshell> JShell jsh = JShell.builder().out(System.out).build();
    jsh ==> jdk.jshell.JShell@1134affc
    
    jshell> var sca = jsh.sourceCodeAnalysis()
    sca ==> jdk.jshell.SourceCodeAnalysisImpl@73f792cf
    
    jshell> sca.highlights("System.out.println(\"");
    | Exception java.lang.IllegalArgumentException
    | at JCDiagnostic.<init> (JCDiagnostic.java:659)
    | at JCDiagnostic.<init> (JCDiagnostic.java:641)
    | at JCDiagnostic$Factory.create (JCDiagnostic.java:294)
    | at JCDiagnostic$Factory.error (JCDiagnostic.java:111)
    | at AbstractLog.error (AbstractLog.java:144)
    | at JavaTokenizer.lexError (JavaTokenizer.java:201)
    | at JavaTokenizer.scanString (JavaTokenizer.java:470)
    | at JavaTokenizer.readToken (JavaTokenizer.java:1017)
    | at Scanner.nextToken (Scanner.java:124)
    | at SourceCodeAnalysisImpl.lambda$highlights$0 (SourceCodeAnalysisImpl.java:680)
    | at TaskFactory.lambda$runTask$1 (TaskFactory.java:218)
    | at JavacTaskPool.getTask (JavacTaskPool.java:193)
    | at TaskFactory.runTask (TaskFactory.java:211)
    | at TaskFactory.analyze (TaskFactory.java:180)
    | at TaskFactory.analyze (TaskFactory.java:166)
    | at TaskFactory.analyze (TaskFactory.java:155)
    | at SourceCodeAnalysisImpl.highlights (SourceCodeAnalysisImpl.java:651)
    | at (#4:1)