Steps to Reproduce

1. Implement the method as defined in networkextension.cs
2. Attempt to pass a null value to the completion handler.

Expected Behavior

Null values should be able to be passed to the completion handler. This is implied in the Obj-C declaration, but is explicit in the swift declaration.

func handleAppMessage(
    _ messageData: Data,
    completionHandler: ((Data?) -> Void)? = nil
)

Actual Behavior

If implement as defined in the C# NETunnelProvider interface null values are not allowed to be passed to the competition handler.
This can be worked around by modifying the overridden method signature (below) to allow null values to be passed, but this results in a compiler warning.

public override void HandleAppMessage(NSData messageData, Action<NSData?>? completionHandler)
{
}

Environment

Visual Studio for Mac
17.5 Preview (17.5 build 437)

Build Logs

<redacted>/PacketTunnelProvider.cs(91,26): warning CS8610: Nullability of reference types in type of parameter 'completionHandler' doesn't match overridden member. [<redacted>.csproj::TargetFramework=net7.0-ios]