Validate a GUID in C#: .NET 10, null-safe validators

[vladimir-pecanac-main]

Sample update for the article "Validate a GUID in C# With Guid.TryParse" (https://code-maze.com/csharp-how-to-validate-a-guid/).

Changes, all inside csharp-classes-struct-record/HowToValidateGuid:

• Both projects move from net8.0 to net10.0.
• Nullable reference types enabled in both projects (was disable).
• GuidHelper: all six validators take string? input. ValidateWithGuidParse, ValidateWithGuidParseExact and ValidateWithNewGuid catch ArgumentNullException as well as FormatException (catch (Exception ex) when (ex is FormatException or ArgumentNullException)), because Guid.Parse(null), Guid.ParseExact(null, "D") and new Guid(null) throw ArgumentNullException. ValidateWithRegex returns false for null instead of throwing from Regex.IsMatch.
• The benchmark class moves from the HowToUseStringPool.Benchmark namespace (copied from another sample) to HowToValidateGuid.Benchmark, in HowToValidateGuidBenchmark.cs and Program.cs.
• GuidHelperTests: the fixture field is initialised at its declaration, which clears CS8618 now that nullable is on.
• Eight new tests (18 to 26): a null-input test for each of the six validators, and an X-format test for ValidateWithGuidParseExact and ValidateWithGuidTryParseExact.
• New GuidHelper.IsUsableGuid (true only for a string that parses as a GUID and is not Guid.Empty), as the article shows it, with four tests: null, a random string and Guid.Empty return false, a real GUID returns true (26 to 30).

Package versions, re-queried on NuGet on 2026-10-11 (latest listed stable):

• BenchmarkDotNet 0.15.8
• Microsoft.NET.Test.Sdk 18.10.1
• MSTest.TestAdapter 4.5.1
• MSTest.TestFramework 4.5.1
• coverlet.collector 10.1.0
• AutoFixture 4.18.1

Local results on SDK 10.0.302 / runtime 10.0.10: dotnet build -c Release 0 warnings 0 errors; dotnet test 30 passed, 0 failed; dotnet list package --vulnerable --include-transitive reports no vulnerable packages in either project.