fix(flags): handle null early_exit values

[dustinbyrne]

💡 Motivation and Context

Fixes #311.

The /flags/definitions response can contain filters.early_exit: null. The SDK modeled this field as a non-nullable boolean, so System.Text.Json rejected the response before local feature flag evaluation could begin.

This makes the internal field nullable while preserving false as the absent-field default. The evaluator already normalizes null to false, so explicit null values now follow the existing non-early-exit path without changing true, false, or omitted-field behavior.

A patch changeset covers PostHog. There are no public API or default-behavior changes.

💚 How did you test it?

• Reproduced the issue with a regression case that failed before the fix with JsonException: The JSON value could not be converted to System.Boolean.
• Extended the existing JSON-backed early-exit test to verify both true and null, including the resulting local evaluation behavior.
• dotnet restore --locked-mode
• bin/fmt --check
• dotnet build --configuration Release --no-restore --nologo (0 warnings, 0 errors)
• dotnet test --configuration Release --no-build --nologo --framework net8.0
  • UnitTests: 1,141 passed, 2 skipped
  • UnitTests.AspNetCore: 50 passed
  • PostHog.AI.Tests: 19 passed

The .NET Core 3.1 test binary builds successfully, but its tests were not run locally because the x64 .NET Core 3.1 host is not installed in this environment.

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran pnpm changeset to generate a changeset file

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Pi coding agent (openai-codex/gpt-5.6-sol) traced and reproduced the reported serialization failure, implemented the scoped fix test-first, and ran the Simplify skill. A fresh-context builtin reviewer found no blockers and suggested exercising evaluation after deserialization; the final regression theory covers that path for both true and null.

[github-actions]

posthog-dotnet Compliance Report

Date: 2026-09-02 14:44:48 UTC
Duration: 4253ms

✅ All Tests Passed!

17/17 tests passed

---

Feature_Flags Tests

✅ 17/17 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	225ms
Request Payload.Flags Request Uses V2 Query Param	✅	125ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	110ms
Request Payload.Flags Request Omits Authorization Header	✅	109ms
Request Payload.Token In Flags Body Matches Init	✅	108ms
Request Payload.Groups Round Trip	✅	111ms
Request Payload.Groups Default To Empty Object	✅	109ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	108ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	109ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	108ms
Request Lifecycle.No Flags Request On Init Alone	✅	3ms
Request Lifecycle.No Flags Request On Normal Capture	✅	113ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	213ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	110ms
Retry Behavior.Retries Flags On 502	✅	1114ms
Retry Behavior.Retries Flags On 504	✅	1111ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	211ms

[greptile-apps]

_{Reviews (1): Last reviewed commit: "chore: add PostHog.AspNetCore changeset" | Re-trigger Greptile}