Fix ParsingException in cases of null file parameter

[jepst]

The comment for the constructor indicates that the file parameter can be null, but the constructMessage method will NPE if file is null.

This fixes the following: the 5.0 build crashes for me when running under OpenJDK 22 as follows:

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "java.io.File.toString()" because "file" is null
	at de.jplag.ParsingException.constructMessage(ParsingException.java:79)
	at de.jplag.ParsingException.<init>(ParsingException.java:31)
	at de.jplag.java.JavacAdapter.lambda$processErrors$1(JavacAdapter.java:80)
	at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:212)
	at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:194)
	at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1709)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:556)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:546)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:622)
	at java.base/java.util.stream.AbstractPipeline.evaluateToArrayNode(AbstractPipeline.java:291)
	at java.base/java.util.stream.ReferencePipeline.toArray(ReferencePipeline.java:631)
	at java.base/java.util.stream.ReferencePipeline.toArray(ReferencePipeline.java:637)
	at java.base/java.util.stream.ReferencePipeline.toList(ReferencePipeline.java:642)
	at de.jplag.java.JavacAdapter.processErrors(JavacAdapter.java:81)
	at de.jplag.java.JavacAdapter.parseFiles(JavacAdapter.java:58)
	at de.jplag.java.Parser.parse(Parser.java:24)
	at de.jplag.java.JavaLanguage.parse(JavaLanguage.java:48)
	at de.jplag.Submission.parse(Submission.java:255)
	at de.jplag.SubmissionSet.parseSubmissions(SubmissionSet.java:159)
	at de.jplag.SubmissionSet.parseAllSubmissions(SubmissionSet.java:111)
	at de.jplag.SubmissionSet.<init>(SubmissionSet.java:49)
	at de.jplag.SubmissionSetBuilder.buildSubmissionSet(SubmissionSetBuilder.java:102)
	at de.jplag.JPlag.run(JPlag.java:73)
	at de.jplag.cli.CLI.runJPlag(CLI.java:132)
	at de.jplag.cli.CLI.main(CLI.java:92)

[sonarqubecloud]

Quality Gate passed for 'JPlag Plagiarism Detector'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

[tsaglam]

Looks good, thanks for your fix.