NPE in Item.enrichProductFromVATBreakdown breaks validation in 2.25.0 (regression vs 2.24.0)

## Summary Validating an existing Factur-X/ZUGFeRD PDF (EN16931 comfort profile) with Mustang-CLI 2.25.0 aborts with a NullPointerException during import. The resulting report has `<xml summary status="invalid">` and root `<summary status="invalid">`, although schema and Schematron validation themselves report no failed assertions -- the notices emitted are identical to those from 2.24.0. The same files validate as `valid` with Mustang-CLI 2.24.0. ## Environment - Mustang-CLI 2.25.0 (Implementation-Version from MANIFEST.MF) - Eclipse Temurin JDK 21.0.11+10, Windows Server - Command: `java -jar Mustang-CLI-2.25.0.jar --action validate --source <file>` ## Observed Out of 608 previously delivered invoices, 3 fail this way under 2.25.0 and pass under 2.24.0. All other verdicts are byte-for-byte identical between the two versions (input files verified unchanged via SHA-1). [main] ERROR org.mustangproject.ZUGFeRD.ZUGFeRDInvoiceImporter - Failed to parse PDF java.lang.NullPointerException: Cannot read field "scale" because "val" is null at java.base/java.math.BigDecimal.compareTo(BigDecimal.java:3130) at org.mustangproject.Item.enrichProductFromVATBreakdown(Item.java:402) at org.mustangproject.ZUGFeRD.ZUGFeRDInvoiceImporter.extractInto(ZUGFeRDInvoiceImporter.java:1080) at org.mustangproject.ZUGFeRD.ZUGFeRDInvoiceImporter.setDocument(ZUGFeRDInvoiceImporter.java:369) at org.mustangproject.ZUGFeRD.ZUGFeRDInvoiceImporter.setRawXML(ZUGFeRDInvoiceImporter.java:307) at org.mustangproject.ZUGFeRD.ZUGFeRDInvoiceImporter.setRawXML(ZUGFeRDInvoiceImporter.java:321) at org.mustangproject.ZUGFeRD.ZUGFeRDInvoiceImporter.extractFiles(ZUGFeRDInvoiceImporter.java:280) at org.mustangproject.ZUGFeRD.ZUGFeRDInvoiceImporter.extractLowLevel(ZUGFeRDInvoiceImporter.java:183) at org.mustangproject.ZUGFeRD.ZUGFeRDInvoiceImporter.setInputStream(ZUGFeRDInvoiceImporter.java:130) at org.mustangproject.validator.PDFValidator.validate(PDFValidator.java:147) The report contains the exception as `<exception type="22">`. ## Note on `--no-arithmetic-check` With `--no-arithmetic-check` the verdict returns to `valid` (root, xml and pdf), but the NullPointerException is still logged to stderr. So the crash happens regardless; the flag only suppresses its effect on the verdict. ## Expected Either the importer should tolerate the null value, or -- if the input really is invalid -- the report should say which business term is at fault instead of surfacing a NullPointerException. I can provide a redacted sample document by e-mail if that helps.