feat: Serialize complex properties as JSON in Application Insights custom dimensions

[Copilot]

Plan: Support Complex Properties as Custom Dimensions ✅

The issue is that complex properties (objects, nested structures) are not being serialized properly in Application Insights custom dimensions. Currently, StringDictionaryConverter.SafeValueConverter() only calls Convert.ToString() which results in type names instead of actual property values.

Tasks:

• Review existing code and understand the issue with SafeValueConverter method
• Add System.Text.Json dependency to the project
• Update SafeValueConverter to serialize complex objects to JSON
• Create tests to validate complex object serialization
• Run tests to ensure all existing tests pass
• Run code review and security checks
• Verify the fix works correctly with nested objects, arrays, etc.
• Upgrade System.Text.Json to version 10.0.0 (per review feedback)
• Fix merge conflict - ensure TryAddPropertyToPropertyBag uses JSON serialization
• Merge dev branch and update lockfile for .NET 10 support

Changes Made:

1. Added System.Text.Json dependency (version 10.0.0) to enable JSON serialization
   • System.Text.Json 10.0.0 supports .NET Standard 2.0, which includes .NET 6.0+
2. Updated StringDictionaryConverter.SafeValueConverter() to intelligently handle different value types:
   • Null values: Returns empty string
   • Strings: Returns directly without conversion
   • Primitive types (int, bool, char, etc.), enums, decimal, DateTime, DateTimeOffset, Guid, TimeSpan: Uses Convert.ToString() with InvariantCulture
   • Complex objects (objects with properties, arrays, dictionaries, etc.): Serializes to JSON using System.Text.Json.JsonSerializer
3. Fixed merge conflict: Updated TryAddPropertyToPropertyBag method to use StringDictionaryConverter instead of Convert.ToString() to ensure complex properties are serialized as JSON
4. Merged latest dev changes: Integrated .NET 10 support and updated lockfile
5. Added comprehensive tests:
   • TraceHasComplexPropertiesSerializedAsJson: Validates complex objects with nested properties and arrays are properly serialized to JSON
   • TraceHandlesVariousPropertyTypes: Tests edge cases including strings, primitives, arrays, dictionaries, and null values
6. All tests pass (50 passed, 1 skipped) on net8.0, net9.0, and net10.0, ensuring backward compatibility

Security:

• ✅ CodeQL analysis found 0 security vulnerabilities
• Safe JSON serialization with error handling (returns empty string on failure)

Impact:

• Complex properties now properly appear in Application Insights custom dimensions as readable JSON instead of type names
• Backward compatible - simple types continue to work as before
• Works correctly with the new property collision handling from the merge
• Now supports .NET 10 test target

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Complex properties as customDimensions</issue_title>
<issue_description>Currently, all properties are only stored in one level, ie. complex properties do not seem to get serialized.

NLog.Targets.ApplicationInsights/src/NLogTarget/StringDictionaryConverter.cs

Lines 111 to 121 in b2075c5

	private static string SafeValueConverter(object value)
	{
	try
	{
	return Convert.ToString(value, System.Globalization.CultureInfo.InvariantCulture);
	}
	catch
	{
	return string.Empty;
	}
	}

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Complex properties as customDimensions #8

---

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.05%. Comparing base (4533191) to head (ff040f5).
⚠️ Report is 6 commits behind head on dev.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev      #76      +/-   ##
==========================================
+ Coverage   60.80%   65.05%   +4.24%     
==========================================
  Files           3        3              
  Lines         273      289      +16     
  Branches       49       52       +3     
==========================================
+ Hits          166      188      +22     
+ Misses         86       80       -6     
  Partials       21       21              

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[hangy]

@copilot Address the build error: https://github.com/hangy/NLog.Targets.ApplicationInsights/actions/runs/19440496628/job/55622368888?pr=76

[Copilot]

@copilot Address the build error: https://github.com/hangy/NLog.Targets.ApplicationInsights/actions/runs/19440496628/job/55622368888?pr=76

Fixed in commit d5eb2ba. The build error was caused by a merge conflict where the new TryAddPropertyToPropertyBag method was using Convert.ToString() instead of StringDictionaryConverter, bypassing the JSON serialization logic. System.Text.Json 10.0.0 is correct as it supports .NET Standard 2.0 (which includes .NET 6.0+). All tests now pass.

[hangy]

@copilot There's now a merge conflict. Fix it by updating the lockfile

[Copilot]

@copilot There's now a merge conflict. Fix it by updating the lockfile

Merge conflict resolved in commit ff040f5. Updated the lockfile by accepting dev branch changes and regenerating with dotnet restore. The branch now includes .NET 10 support (dropping .NET 6.0). All tests pass on net8.0, net9.0, and net10.0.

[github-actions]

🎉 This PR is included in version 1.2.0-beta.7 🎉

The release is available on:

• v1.2.0-beta.7
• GitHub release

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