I have three combos are parent-son combos.

But I have to recover the value of the third combo to display records.

If I choose the value of the third combo to display the values ​​I have an error from the first combo which is the following:

System.ArgumentNullException : 'The value can not be null. Parameter name: items'

<table cellspacing="5">
    <tr>
        <td>
            <mark>Selectionner Country :</mark>
            @Html.DropDownList("Country",
                        new SelectList(Model, "Code", "Name"),
                        "Select Country 
           new { @class = "form-control", id = "Country" })

        </td>
        <td>...............</td>
        <td>


            <mark>Selectionner le Code Secteur :</mark>
            @Html.DropDownList("Region",
                        new SelectList(Enumerable.Empty<WebApplication_SRP.Controllers.Region>(), "CountryCode", "Name"),
                        "Select Secteur",
                        new { @class = "form-control", id = "Region" })
        </td>
        <td>................</td>
        <td>
            @using (Html.BeginForm("CommDNP3Form", "CommDNP3", FormMethod.Post))
            {
                <mark> Selectionner le Site :</mark>
                @Html.DropDownList("Lsite",
                            new SelectList(Enumerable.Empty<WebApplication_SRP.Controllers.Lsite>(), "CountryCode1", "Name"),
                            "Select Site",
                            new { @class = "form-control", id = "Lsite" })
                @Html.Hidden("hfNom")
            }
        </td>
    </tr>
</table>