RecorderManager.CreateMockedObject bug or feature

namespace test
{
    public class DBHelper
    {
        public static SqlConnection GetConnection()
        {
            return new SqlConnection();
        }
    }

    public class TestClass
    {
        public static void GetProductivityReportData(
            DateTime start_date,
            DateTime end_date)
        {
            using (SqlConnection sql_conn = DBHelper.GetConnection())
            {
                SqlCommand sqlCmd = new SqlCommand("BvSpRptProdByInterEx2", sql_conn);
                
                sqlCmd.Parameters.AddWithValue("@StartDate", start_date);
                sqlCmd.Parameters.AddWithValue("@EndDate", end_date);
            }
        }
    }

    [TestClass]
    public class Class1
    {
        [TestCleanup]
        public void TestCleanup()
        {
            MockManager.ClearAll();
        }

        [TestInitialize]
        public void TestInitialize()
        {
            MockManager.Init();
        }

        [TestMethod]
        public void Test1()
        {
            Bar(true);
        }

        [TestMethod]
        public void Test2()
        {
            Bar(false);
        }

        public void Bar(bool mockSqlParameter)
        {
            DateTime startDate = DateTime.Now;
            DateTime endDate = DateTime.Now;

            if (mockSqlParameter)
            {
                SqlParameterCollection mockedParams = RecorderManager.CreateMockedObject<SqlParameterCollection>();
            }

            using (RecordExpectations recorder = new RecordExpectations())
            {
                SqlConnection conn = DBHelper.GetConnection();
                recorder.ReturnDefaultImplementation();

                conn.Dispose();

                SqlCommand sqlCmd = new SqlCommand("", conn);
                recorder.ReturnDefaultImplementation().CheckArguments("BvSpRptProdByInterEx2", Check.IsAny());

                recorder.ExpectAndReturn(sqlCmd.Parameters.AddWithValue("@StartDate", startDate), null);
                recorder.CheckArguments("@StartDate", startDate);
            }

            TestClass.GetProductivityReportData(startDate, endDate);
        }
    }
}

------ Test started: Assembly: delete.dll ------

TestCase 'test.Class1.Test2'
failed: System.NullReferenceException: Object reference not set to an instance of an object.
at System.Data.SqlClient.SqlParameterCollection.ValidateType(Object value)
at System.Data.SqlClient.SqlParameterCollection.Add(Object value)
at System.Data.SqlClient.SqlParameterCollection.Add(SqlParameter value)
at System.Data.SqlClient.SqlParameterCollection.AddWithValue(String parameterName, Object value)
D:!6deleteClass1.cs(29,0): at test.TestClass.GetProductivityReportData(DateTime start_date, DateTime end_date)
D:!6deleteClass1.cs(85,0): at test.Class1.Bar(Boolean mockSqlParameter)
D:!6deleteClass1.cs(58,0): at test.Class1.Test2()


0 passed, 1 failed, 0 skipped, took 6,27 seconds.