抛出异常

System.InvalidCastException:“无法将类型”System.Data.Linq.Table“”1[SalesWithLinq.DAL.UnitName]“”的对象强制转换为类型“System.Collections.Generic.List”“1[SalesWithLinq.DAL.UnitName]”“。”
我想在存储库中添加单元名称lookUpEdit并保存它，一旦我离开单元格，数据将成功保存在数据库中，但当到达铸造行时，抛出异常

RepositoryItemLookUpEdit repoUOM = new RepositoryItemLookUpEdit(); // field of form class

repoUOM.DisplayMember = "Name"; // inside form load event
repoUOM.ValueMember = "ID"; // inside form load event
repoUOM.TextEditStyle = DevExpress.XtraEditors.Controls.TextEditStyles.Standard; // inside form load event

private void RepoUOM_ProcessNewValue(object sender, DevExpress.XtraEditors.Controls.ProcessNewValueEventArgs e)
{
    if (e.DisplayValue is string value && value.Trim() != string.Empty)
    {
        var NewObject = new UnitName() { Name = value.Trim() };
        using (var db = new dbDataContext())
        {
            db.UnitNames.InsertOnSubmit(NewObject);
            db.SubmitChanges();
        }

        ((List<UnitName>)repoUOM.DataSource).Add(NewObject); // exception thrown here
        e.Handled = true;
    }
}