C#, Enumeration nullReferenceException was not handled.

namespace mip
{
    public enum enumMessageType
    {
        mtA, mtB, mtC, ...
    }
afterthought

namespace mipTest
{
    public partial class Form 1:Form
    {
        private void btnInsert_Click(object sender, EventArgse)
        {
            QueueInfo qi = new QueueInfo();
            qi.CommandInfo.MessageType=enumMessageType.mtA;←This is where the error occurs.
            afterthought