C# Sortable DatagridView doesn't cast to object

I use Dapper to bind data to my dataGridView. To fill the dataGridView I receive IEnumerable but this is not sortable. So I use the following method.

    public static DataTable ToDataTable<T>(this IEnumerable<T> collection)
    {
        DataTable dt = new DataTable("DataTable");
        Type t = typeof(T);
        PropertyInfo[] pia = t.GetProperties();

        //Inspect the properties and create the columns in the DataTable
        foreach (PropertyInfo pi in pia)
        {
            Type ColumnType = pi.PropertyType;
            if ((ColumnType.IsGenericType))
            {
                ColumnType = ColumnType.GetGenericArguments()[0];
            }
            dt.Columns.Add(pi.Name, ColumnType);
        }

        //Populate the data table
        foreach (T item in collection)
        {
            DataRow dr = dt.NewRow();
            dr.BeginEdit();
            foreach (PropertyInfo pi in pia)
            {
                if (pi.GetValue(item, null) != null)
                {
                    dr[pi.Name] = pi.GetValue(item, null);
                }
            }
            dr.EndEdit();
            dt.Rows.Add(dr);
        }
        return dt;
    }

This works so far. But I want to use the doubleClick to select a single object from the dataGridView. Until I used the above method ToDataTable I get the object data this way:

 private void dataGridView1_CellDoubleClick(object sender, DataGridViewCellEventArgs e)
    {
        if (e.RowIndex != -1)
        {
            obj = dataGridView1.Rows[e.RowIndex].DataBoundItem as Part;
            ...

But now the object always return null.

What do I have to do to get furthermore an object from doubleClick dataGridView?