Enable nullable reference types and resolve warnings

[JSv4]

Summary

The codebase currently has <Nullable>disable</Nullable> in the project file and suppresses CS8632 warnings. We should enable nullable reference types and properly annotate the codebase for improved null safety.

Current State

• Docxodus.csproj has <Nullable>disable</Nullable>
• CS8632 warnings are suppressed via <NoWarn>$(NoWarn);CS8073;CA2200;CS8632</NoWarn>
• Some files already have nullable annotations (?) but without the nullable context enabled

Scope

Enabling nullable produces ~9,000 warnings across 61 source files. The most common issues:

Warning	Description	Count
CS8600	Converting possible null to non-nullable type	~3,100
CS8602	Dereference of possibly null reference	~2,300
CS8604	Possible null reference argument	~1,500
CS8618	Non-nullable field uninitialized in constructor	~600
CS8625	Cannot convert null literal to non-nullable type	~570
CS8603	Possible null reference return	~530

Recommended Approach

An incremental file-by-file approach is best:

1. Add #nullable enable at the top of individual files
2. Fix warnings in that file (add ? annotations, null checks, or ! where safe)
3. Run tests to verify behavior unchanged
4. Repeat for next file

Start with smaller, simpler files to build momentum.

Work Required

1. Incrementally enable nullable per-file with #nullable enable
2. Add appropriate nullable annotations to public APIs
3. Fix or suppress nullable warnings in legacy code
4. Once all files are done, enable <Nullable>enable</Nullable> in csproj
5. Remove CS8632 from NoWarn

Files to Prioritize

Smaller utility files first, then tackle the larger ones:

• PtOpenXmlUtil.cs - many nullable issues (large file)
• WmlToHtmlConverter.cs - ImageInfo class fields
• WmlComparer.cs - comparison unit classes

Labels

• enhancement
• tech-debt

[JSv4]

Updated CLAUDE.md with coding standards requiring #nullable enable for new files and substantial refactors. This ensures we progressively improve null safety without needing to fix all 9,000 warnings at once.

See commit 6b1c65c.