Fix cert-sign API NullPointerException when pageNumber is omitted for invisible signatures

[Ludy87]

Description of Changes

Please provide a summary of the changes, including:

• What was changed

  • Updated SignPDFWithCertRequest to use Boolean for showSignature and showLogo, and made pageNumber nullable.
  • In CertSignController:
    • Added an @InitBinder to convert empty multipart fields to null.
    • Extended @PostMapping to consume both multipart/form-data and application/x-www-form-urlencoded.
    • Wrapped pageNumber calculation in a null-check (pageNumber = request.getPageNumber() != null ? request.getPageNumber() - 1 : null).
    • Changed signature-visualization and logo checks to Boolean.TRUE.equals(...) to avoid unboxing NPE.
  • Cleaned up imports and schema annotations in the request model.

• Why the change was made

  • Prevent a 500 Internal Server Error caused by calling .intValue() on a null pageNumber when showSignature=false (invisible signatures).
  • Ensure that omitting pageNumber doesn’t break clients using the “try it out” swagger UI or curl-based requests.

• Any challenges encountered

  • Configuring Spring’s data binder to treat empty file inputs as null required a custom PropertyEditorSupport.
  • Balancing backward compatibility with stricter type handling (switching from primitive boolean to boxed Boolean).

Closes #3459

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Checklist

General

• I have read the Contribution Guidelines
• I have read the Stirling-PDF Developer Guide (if applicable)
• I have read the How to add new languages to Stirling-PDF (if applicable)
• I have performed a self-review of my own code
• My changes generate no new warnings

Documentation

• I have updated relevant docs on Stirling-PDF's doc repo (if functionality has heavily changed)
• I have read the section Add New Translation Tags (for new translation tags only)

UI Changes (if applicable)

• Screenshots or videos demonstrating the UI changes are attached (e.g., as comments or direct attachments in the PR)

Testing (if applicable)

• I have tested my changes locally. Refer to the Testing Guide for more details.

[Copilot]

Pull Request Overview

This PR addresses the NullPointerException occurring when pageNumber is omitted for invisible signatures by improving type handling and null-safety in the cert-sign API. Key changes include:

• Converting the showSignature and showLogo fields from primitives to boxed Booleans and allowing pageNumber to be nullable.
• Adding a custom @InitBinder in CertSignController to convert empty multipart fields to null and updating the endpoint method to consume both multipart form data and urlencoded content.
• Wrapping pageNumber calculation with a null-check and using Boolean.TRUE.equals for null-safe comparisons.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/main/java/stirling/software/SPDF/model/api/security/SignPDFWithCertRequest.java	Updated schema annotations and field types for improved null handling in the request model.
src/main/java/stirling/software/SPDF/controller/api/security/CertSignController.java	Added a custom property editor, extended POST mapping consumption types, and updated signature/logic checks to prevent NPE.

Comments suppressed due to low confidence (1)

src/main/java/stirling/software/SPDF/controller/api/security/CertSignController.java:90

• [nitpick] Consider adding a clarifying comment on the custom PropertyEditorSupport registration to explain that any provided text for a MultipartFile is intentionally treated as null. This will help future maintainers understand the rationale behind this configuration.

binder.registerCustomEditor( MultipartFile.class, new PropertyEditorSupport() { ... }

[Ludy87]

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[Ludy87]

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@thepebbler try this PR, the link reflects this PR, you can try