Add test pinning RegisterUlid's Nullable<Ulid> handler registration

src/Dapper.IntegrationTests/DapperUlidTypeHandlerRegistrationTests.cs

@@ -0,0 +1,43 @@
+using Microsoft.Data.Sqlite;
+using Dapper;
+
+namespace ByteAether.Ulid.Dapper.IntegrationTests;
+
+public class DapperUlidTypeHandlerRegistrationTests : IDisposable
+{
+	private readonly SqliteConnection _connection;
+
+	public DapperUlidTypeHandlerRegistrationTests()
+	{
+		_connection = new("Data Source=:memory:");
+		_connection.Open();
+	}
+
+	[Fact]
+	public async Task RegisterUlid_ShouldRegisterHandler_ForNullableUlidParametersAndResults()
+	{
+		// Arrange
+		SqlMapper.ResetTypeHandlers();
+		DapperUlid.RegisterUlid(UlidStorageFormat.String);
+
+		Ulid? value = Ulid.New();
+
+		// Act - A bare scalar query exercises Dapper's parameter-building and result-materialization
+		// pipeline directly against a `Ulid?`-typed parameter/result, without going through an entity
+		// or a table. This pins that `RegisterUlid` makes `Nullable<Ulid>` resolve to the same
+		// type handler as `Ulid`, instead of relying on incidental coverage from the broader
+		// entity round-trip tests.
+		var roundTripped = await _connection.ExecuteScalarAsync<Ulid?>("SELECT @Value AS Value", new { Value = value });
+		var roundTrippedNull = await _connection.ExecuteScalarAsync<Ulid?>("SELECT @Value AS Value", new { Value = (Ulid?)null });
+
+		// Assert
+		Assert.Equal(value, roundTripped);
+		Assert.Null(roundTrippedNull);
+	}
+
+	public void Dispose()
+	{
+		_connection.Dispose();
+		GC.SuppressFinalize(this);
+	}
+}