Enable nullable reference types and improve null handling across multiple files

[Shane32]

No changes to public API -- NRT was already enabled there.

Summary by CodeRabbit

• Chores
  • Enabled nullable reference types project-wide for stricter nullability checks.

[coderabbitai]

📝 Walkthrough

Walkthrough

Enables nullable reference types globally via Directory.Build.props, removes per-project Nullable setting from QRCoder.csproj, updates console and demo apps for null-safe handling and minor UI change, and adjusts tests to use null-forgiving operators and safer null checks. One helper adds a null-safe assembly location fallback.

Changes

Cohort / File(s)	Summary
Centralized nullable configuration Directory.Build.props, QRCoder/QRCoder.csproj	Add <Nullable>enable</Nullable> at the solution level; remove redundant Nullable setting from project file.
Console app nullability and flow guard QRCoderConsole/Program.cs	Make fileName and text nullable; require both text and outputFileName to be non-null before generating QR.
Demo app null-safety and UI tweak QRCoderDemo/Form1.cs	Null-safe ECC level selection with default "L"; change PictureBox mode to StretchImage; make GetIconBitmap return Bitmap?; allow null icon; imageFormat becomes nullable.
Tests: nullability and reflection tightening QRCoderTests/Helpers/HelperFunctions.cs, QRCoderTests/PayloadGeneratorTests/IbanTests.cs, QRCoderTests/PayloadGeneratorTests/RussiaPaymentOrderTests.cs, QRCoderTests/QRGeneratorTests.cs	Helper: null-safe assembly Location with fallback to empty string. Tests: add null-forgiving operators to reflection calls and nullable locals; no behavioral changes.

Sequence Diagram(s)

sequenceDiagram
  autonumber
  actor User
  participant Program as Console Program
  participant QR as QR Generator

  User->>Program: Provide text and outputFileName
  alt text != null AND outputFileName != null
    Program->>QR: Generate QR from text
    QR-->>Program: Bitmap
    Program-->>User: Save to outputFileName
  else missing input/path
    Program-->>User: Skip generation / exit
  end

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Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• Cleanup project files; configure Directory.Build.props #628 — Also edits Directory.Build.props for build metadata; related by central build configuration changes.

Suggested reviewers

• gfoidl

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title Check	✅ Passed	The title accurately and concisely summarizes the primary change of enabling nullable reference types and enhancing null handling across the codebase, which aligns with the PR’s content and objectives, making it clear for reviewers scanning the history.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch nrt

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📜 Recent review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 84f4906 and 8ea5ea1.

📒 Files selected for processing (8)

• Directory.Build.props (1 hunks)
• QRCoder/QRCoder.csproj (0 hunks)
• QRCoderConsole/Program.cs (3 hunks)
• QRCoderDemo/Form1.cs (3 hunks)
• QRCoderTests/Helpers/HelperFunctions.cs (1 hunks)
• QRCoderTests/PayloadGeneratorTests/IbanTests.cs (5 hunks)
• QRCoderTests/PayloadGeneratorTests/RussiaPaymentOrderTests.cs (1 hunks)
• QRCoderTests/QRGeneratorTests.cs (6 hunks)

💤 Files with no reviewable changes (1)

• QRCoder/QRCoder.csproj

🧰 Additional context used

🧬 Code graph analysis (2)

QRCoderTests/QRGeneratorTests.cs (1)

QRCoder/QRCodeGenerator/AlphanumericEncoder.cs (1)

• Dictionary (27-40)

QRCoderDemo/Form1.cs (3)

QRCoderTests/Helpers/HelperFunctions.cs (2)

• Bitmap (30-39)
• Bitmap (93-99)

QRCoder/ArtQRCode.cs (6)

• Bitmap (37-38)
• Bitmap (45-46)
• Bitmap (62-129)
• Bitmap (138-162)
• Bitmap (208-232)
• Bitmap (281-290)

QRCoder/QRCode.cs (5)

• Bitmap (34-35)
• Bitmap (45-46)
• Bitmap (56-87)
• Bitmap (101-148)
• Bitmap (197-203)

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (2)

• GitHub Check: additional-tests
• GitHub Check: build

🔇 Additional comments (12)

QRCoderTests/PayloadGeneratorTests/IbanTests.cs (1)

23-23: LGTM! Null-forgiving operators added for reflection-based test calls.

The null-forgiving operators (!) are correctly applied to suppress nullable warnings in reflection-based test code where method existence is guaranteed by the test setup.

Also applies to: 34-34, 45-45, 56-56, 67-67

QRCoderConsole/Program.cs (3)

23-23: LGTM! Variables correctly made nullable.

The nullable annotations for fileName, outputFileName, and payload are appropriate as these variables are conditionally assigned based on command-line arguments.

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100-100: LGTM! Text variable correctly made nullable.

The nullable annotation is correct as text may remain null if none of the input sources (file, payload, stdin) provide data.

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124-124: Good addition: Null check for outputFileName prevents runtime error.

The added null check for outputFileName prevents calling GenerateQRCode when no output path is specified, avoiding a potential NullReferenceException at line 152 (bitmap.Save(outputFileName, actualFormat)).

Directory.Build.props (1)

13-16: LGTM! Nullable reference types enabled project-wide.

The addition of <Nullable>enable</Nullable> correctly enables nullable reference types across all projects that inherit from this Directory.Build.props file. The updated comment accurately reflects this change.

QRCoderTests/PayloadGeneratorTests/RussiaPaymentOrderTests.cs (1)

119-125: LGTM! Correct nullable handling in null validation test.

The nullable annotation on account (line 119) and the null-forgiving operator (line 125) correctly support this test's purpose: verifying that passing null for PersonalAcc throws a RussiaPaymentOrderException. The null-forgiving operator suppresses the compiler warning while the test validates the runtime behavior.

QRCoderTests/Helpers/HelperFunctions.cs (1)

46-46: LGTM! Null-safe assembly location handling.

The null-conditional operator (?.) and null-coalescing operator (??) correctly handle the case where Assembly.GetExecutingAssembly().Location might be null, providing a safe empty string fallback. This aligns with nullable reference types enablement.

QRCoderTests/QRGeneratorTests.cs (1)

26-26: LGTM! Null-forgiving operators correctly applied to reflection-based test code.

The null-forgiving operators (!) are appropriately used throughout the reflection-based test methods where type and member names are known at compile time. This pattern correctly suppresses nullable warnings while maintaining test reliability.

Also applies to: 34-34, 391-392, 404-404, 415-415, 426-426, 437-437

QRCoderDemo/Form1.cs (4)

27-27: LGTM! Null-safe ECC level extraction with sensible default.

The null-conditional operator with null-coalescing fallback (?.ToString() ?? "L") correctly handles the case where comboBoxECC.SelectedItem might be null, defaulting to "L" error correction level.

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39-39: Note: Display mode changed from CenterImage to StretchImage.

This appears to be an intentional UI behavior change. The QR code will now stretch to fill the PictureBox rather than being centered at its natural size.

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42-56: LGTM! GetIconBitmap return type correctly made nullable.

The nullable return type (Bitmap?) accurately reflects that this method can return null when no icon path is specified (line 46) or when loading fails (line 54). This is compatible with the QRCode.GetGraphic method signature which accepts Bitmap? icon.

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101-108: LGTM! ImageFormat variable correctly typed as nullable.

The nullable type annotation (ImageFormat?) aligns with nullable reference types, though all switch branches assign non-null values. The type annotation is appropriate for consistency with NRT patterns.

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[Shane32]

@gfoidl Whoops I merged this before it was approved. Lmk if you have any comments.

[gfoidl]

@Shane32 LGTM (for the record).