Add additional check to avoid cast issues in PdfNumber when accessing bookmarks

[michelezonca]

Hi everyone,
I ran into the following runtime error when accessing a bookmark destination (from a namedDestination):

type 'PdfNull' is not a subtype of type 'PdfNumber?' in type cast

Unfortunately I cann't share the original PDF (probably malformed), but it opens correctly on other viewers.

This PR fixes the issue by adding a simple defensive type check before casting the destination value to PdfNumber, preventing invalid casts when the destination contains PdfNull (or anything else)

[immankumarsync]

Hi @michelezonca,

Thank you for sharing your proposal and providing the patch to resolve the typecasting issue when accessing the destination of a PdfBookmark that contains PdfNull.

We are currently reviewing the proposed change. We will address this issue, and it will be included in the weekly release scheduled for January 27, 2026.

Please note that, although the Flutter PDF library source code is publicly available on GitHub for transparency, we do not accept direct contributions to the repository. This policy ensures consistency and quality across all releases. Nevertheless, your feedback and suggestions are highly valued, and we encourage you to continue sharing ideas through our official support channels.

Thank you for your understanding and continued support.

Regards,
Imman Kumar P

[michelezonca]

Thanks @immankumarsync, sure, I do understand your policy. Feel free to close this or take the usual actions.

I'll wait for that release to update my pubspec and remove my local fork