LINQ value cannot be null on filtering Gridview

Question

Hei,

I have three textboxes outside the Gridview where I can bind him with what it's written in textboxes.

Here is my code

DataSet dataSet = (DataSet)Session["DATASET_admin"];
    var bind_filter_unfinished = from dataRow in dataSet.Tables["bind_filter_unfinished"].AsEnumerable()
                                 where Convert.ToInt32(dataRow["ID"]).ToString().Contains(txtFilterNrSF.Text) &&
                                 dataRow["SENDER_NAME"].ToString().ToLower().Contains(txtFilterSender.Text.ToLower()) &&
                                 dataRow["DELIVERY_DATE"].ToString().ToLower().Contains(txtFilterDispatching.Text.ToLower())
                                 select new LINQ
                                 {
                                     ID = Convert.ToInt32(dataRow["ID"]),
                                     DEL_NAME = dataRow["DEL_NAME"].ToString(),
                                     TR_NAME = dataRow["TR_NAME"].ToString(),
                                     DELIVERY_DATE = dataRow["DELIVERY_DATE"].ToString(),
                                     COMPANY = dataRow["COMPANY"].ToString(),
                                     COUNTRY = dataRow["COUNTRY"].ToString(),

                                     Items = dataRow["Items"].ToString(),
                                     Comments = dataRow["Comments"].ToString(),

                                     SENDER_NAME = dataRow["SENDER_NAME"].ToString(),
                                     STATUS = dataRow["STATUS"].ToString(),
                                     EMERGENCY_TYPE = dataRow["EMERGENCY_TYPE"].ToString(),
                                     SUPERIOR_NAME = dataRow["SUPERIOR_NAME"].ToString(),

                                     Packing = dataRow["Packing"].ToString()
                                 };
    GridViewAdmin.DataSource = bind_filter_unfinished.ToList();
    GridViewAdmin.DataBind();   

I have something written in every textbox but where I end my query it keeps appear this error

An exception of type 'System.ArgumentNullException' occurred in System.Data.DataSetExtensions.dll but was not handled in user code
{"Value cannot be null.\r\nParameter name: source"}