为什么执行该命令时不返回任何结果？

SqlConnection conn = getConnection();
SqlCommand cmd = new SqlCommand();

cmd.CommandType = CommandType.StoredProcedure;
cmd.CommandText = "SP_PSLA_SEARCH"; //The stored procedure gets added
cmd.CommandTimeout = 0;
cmd.Connection = conn;

// Start adding the parameters of the stored procedure
cmd.Parameters.AddWithValue("@usrnm", thisUser.Username);

int constit = 0;

if (thisUser.Constituencies.Count > 0)
{
    foreach (KeyValuePair<int, string> kp in thisUser.Constituencies)
    {
        if (kp.Value == ddlConstituency.SelectedValue.ToString())
        {
            constit = kp.Key;
            break;
        }
    }
}

cmd.Parameters.AddWithValue("@cnstncy", constit);

string pdval = null;
int valtype = 0;

if (rbsearchradios.SelectedIndex == 0)
{
    try
    {
        pdval = searchVal;
        cmd.Parameters.AddWithValue("@Search", DBNull.Value);
        cmd.Parameters.AddWithValue("@pd", int.Parse(pdval));
        cmd.Parameters.AddWithValue("@type", valtype);
    }
    catch
    {
        System.Web.UI.ScriptManager.RegisterStartupScript(this, this.GetType(), "stop", "alert('Invalid PD Number Supplied! Please Provide A Valid Submission.');", true);
        return;
    }
}
else
{
    valtype = 1;
    cmd.Parameters.AddWithValue("@Search", searchVal);
    cmd.Parameters.AddWithValue("@pd", DBNull.Value);
    cmd.Parameters.AddWithValue("@type", valtype);
}

cmd.Parameters.AddWithValue("@app", 1);

conn.Open();                        

// Creates Dataadapter for execution
SqlDataAdapter dp2 = new SqlDataAdapter(cmd);
DataSet ds = new DataSet();

dp2.Fill(ds, "name");

我正在尝试存储过程的参数，并使该存储过程执行并将结果存储到数据集中，但是我什么也没得到。没有例外，只是存储过程没有结果。

这是存储过程：

DECLARE @return_value int

EXEC    @return_value = [dbo].[SP_PSLA_SEARCH] 
            @usrnm = N'tstone',
            @cnstncy = 55,
            @Search = N'primary',
            @pd = NULL,
            @type = 1,
            @app = 1

SELECT  'Return Value' = @return_value
GO