SelectedItem.Text null when postback

I have a DropdownList

Based on the selected text I populate another ddl with

protected void ddlComponentaActivitate_SelectedIndexChanged(Object sender, EventArgs e)
{
    ddlFactorRisc.Items.Clear();
    ddlFactorRisc.Items.Add("Factor de risc");
    using (SqlConnection conn = new SqlConnection(connString))
    {
        string sqlQuery = "SELECT FactorRisc, FRFID FROM tblFactoriRiscFactori WHERE FRCID = @FRCID ORDER BY FactorRisc";
        using (SqlCommand cmd = new SqlCommand(sqlQuery, conn))
        {
            cmd.CommandType = CommandType.Text;
            cmd.Parameters.AddWithValue("@FRCID", ddlComponentaActivitate.SelectedItem.Value);
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            conn.Open();
            DataSet ds = new DataSet();
            da.Fill(ds);
            ddlFactorRisc.DataSource = ds.Tables[0];
            ddlFactorRisc.DataBind();
            conn.Close();
        }
    }
    ActiveTAB.Value = "#TabEvaluare";
}

The second ddl on View with

But when I try to add data to table using FactorRisc as parameter

cmd.Parameters.AddWithValue("@FactorRisc", ddlFactorRisc.SelectedItem.Text);

I have error that say cannot add null. So it seems it will not get the value. Worth to mention I have 2 more ddl on page, one listed below

On screen data is visible but error on postback. Why?