使用Int32强制转换枚举项0时,查询参数值为Null

Enum LogEventType : int
{
    SignIn,
    SignInFailure,
    SignOut,
    ...
}

private static DataTable QueryEventLogSession(DateTime start, DateTime stop)
{
    DataTable entries = new DataTable();

    using (FbConnection conn = new FbConnection(DSN))
    {
        using (FbDataAdapter adapter = new FbDataAdapter(
            "SELECT event_type, event_timestamp, event_details FROM event_log " +
            "WHERE event_timestamp BETWEEN @start AND @stop " +
            "AND event_type IN (@signIn, @signInFailure, @signOut) " +
            "ORDER BY event_timestamp ASC", conn))
        {
            adapter.SelectCommand.Parameters.AddRange(new Object[] {
                new FbParameter("@start", start),
                new FbParameter("@stop", stop),
                new FbParameter("@signIn", (Int32)LogEventType.SignIn),
                new FbParameter("@signInFailure", (Int32)LogEventType.SignInFailure),
                new FbParameter("@signOut", (Int32)LogEventType.SignOut)});

            Trace.WriteLine(adapter.SelectCommand.CommandText);
            foreach (FbParameter p in adapter.SelectCommand.Parameters)
            {
                Trace.WriteLine(p.Value.ToString());
            }

            adapter.Fill(entries);
        }
    }
    return entries;
}