Non-nullable property warning (CS8618): net10.0, MSTest 4, MemberNotNull and field keyword samples

[vladimir-pecanac-main]

Sample update for the article "Non-nullable Property Must Contain a Non-null Value When Exiting Constructor (CS8618)" (https://code-maze.com/csharp-resolve-non-nullable-property-must-contain-a-non-null-value-warning/).

Folder: csharp-basic-topics/NonNullablePropertyMustContainANonNullValueWarning (only this folder changes).

Changes:

• Both projects retargeted from net7.0 to net10.0. Nullable stays enabled.
• Packages, re-queried on NuGet 2026-10-11 (latest listed stable): Microsoft.NET.Test.Sdk 18.10.1, MSTest.TestAdapter 4.5.1, MSTest.TestFramework 4.5.1, coverlet.collector 10.1.0.
• MSTest 4 removed [ExpectedException], so the dereference test now calls Assert.ThrowsExactly and dereferences _address! (the old _address? would have let the test pass vacuously on a null field).
• Both #pragma comments in Address.cs now carry the current CS8618 diagnostic title from the .NET 10 compiler: "Non-nullable field must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring as nullable."
• Address gains Region, a field-keyword property inside the CS8618 pragma block, which still reports CS9264 (the pragma does not cover it), and Town, the field-keyword property resolved with get => field ?? string.Empty.
• New HelperMethod/Address.cs shows [MemberNotNull(nameof(City))] on a helper method shared by two constructors.
• Four new tests: Region is null, Town is empty, and the helper class sets City from both constructors.

Build (SDK 10.0.302, Release): 0 errors, 2 warnings, both deliberate: CS8618 on Address.FirstName and CS9264 on Address.Region. These are the article's demonstrations.
Tests: 11 passed, 0 failed.
dotnet list package --vulnerable --include-transitive: no vulnerable packages in either project.