fix: add null guard in HexSKColorToByteArray to resolve S2259

[devin-ai-integration]

All Submissions:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

New Feature Submissions:

1. Does your submission pass tests?
2. Have you lint your code locally prior to submission?

Changes to Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you successfully ran tests with your changes locally?

---

fix: add null guard in HexSKColorToByteArray to resolve S2259

The HexSKColorToByteArray methods in PdfByteQRCode and BitmapByteQRCode replaced the previous !string.IsNullOrEmpty(...) checks with an explicit string.IsNullOrEmpty(...) guard that throws ArgumentException. This ensures colorString is non-null and non-empty before Substring is called, resolving the SonarCloud S2259 issue reported on the renderer phase.

Build and dotnet test QRCoder.Core.Tests/ -f net10.0 --configuration Release pass locally (502 tests).

Link to Devin session: https://app.devin.ai/sessions/20c92a1bad724f63b8be89a9e195e664
Requested by: @afonsoft

---

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment, CI, and merge conflict monitoring

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[devin-ai-integration]

Devin Review found 2 potential issues.

[devin-ai-integration]

📝 Info: Behavioral change from silent degradation to exception for empty color strings

The old code silently handled empty color strings by producing a zero-length byte array (which would result in corrupted BMP/PDF output). The new code throws ArgumentException instead. While this is a better behavior, it is technically a breaking change for any consumer that previously relied on passing empty strings without getting an exception. I verified all current internal callers (BitmapByteQRCode.cs:52, PdfByteQRCode.cs:72, and the helper classes) and none pass null or empty — they use either hardcoded hex strings like "#000000" or forward user-provided parameters. However, since these are public API methods (GetGraphic at BitmapByteQRCode.cs:50 and PdfByteQRCode.cs:63), external consumers could be affected.

---

Was this helpful? React with 👍 or 👎 to provide feedback.

[devin-ai-integration]

📝 Info: Duplicated HexSKColorToByteArray implementation across two files

The HexSKColorToByteArray method is identically implemented in both BitmapByteQRCode.cs:113-122 and PdfByteQRCode.cs:216-225. This PR applied the same fix to both copies, but the duplication itself is a maintenance risk — future fixes or enhancements would need to be applied in both places. Consider extracting this into a shared utility (e.g., in the Extensions/ folder) to follow the DRY principle.

---

Was this helpful? React with 👍 or 👎 to provide feedback.