Display data in grid view upon search

Hi, currently I am doing a online store application project. In the search page I will need to search for the Item name and details about the items will be populated at the grid view below. However whatever item name i entered in, it will display all the items which is not the right one.
This is the data access logic codes:

 

 public DataSet Get_ItemRecords(string itemName)//search 

        
{
            
SqlCommand cmd_ItemList = new SqlCommand();

            
cmd_ItemList.CommandText = 
"[VRM].[Get_ItemRecords]";
            
cmd_ItemList.CommandType = 
CommandType.StoredProcedure;
            
cmd_ItemList.Parameters.Clear();

            
SqlParameter sqlParaItemName = new SqlParameter("@itemName", 
SqlDbType.VarChar, 
50);
            
sqlParaItemName.Value = 
itemName;
            
cmd_ItemList.Parameters.Add(sqlParaItemName);

DataSet ds_ItemList = 
getDataSet(cmd_ItemList);
           
return ds_ItemList;

        }

This is the stored procedure responsible for retriving data from the sql server 2008:

 

ALTER procedure [VRM].[GET_ItemRecords]

@itemName varchar (50) = NULL

AS 

select * from VRM.IetmTable where (@itemName IS NOT NULL or itemName= 
@itemName)

This is the business logic layer:

 

using System;
using System.Data;
using System.Web.UI;
using 
System.Web.UI.WebControls;
using com.os.database;
using com.os.com;

namespace OnlineStore
{

    public partial class item : 
System.Web.UI.Page
    
{
        private os_database osdb = new 
os_database();
        private String 
viewStateGVName = "gvItem";


       

        //set the const for the ID of the 
GV Checkbox column
        private const 
string GVCHECKBOXCOLID = "selected";


        protected void 
Page_Load(object sender, EventArgs 
e)
        
{
            if 
(!IsPostBack)
            
{
                
//Set the 
sortExpression
                
ViewState[this.ToString() + "_SortExpression"] = 
"ItemName";
                
ViewState[this.ToString() + "_SortDirection"] = "ASC";

            
}
        
}
        protected void 
btnClear_Click(object sender, EventArgs 
e)
        
{
            
gvItem.Visible = 
false;
            
tbSearchItemName.Text = "";

        }

        protected void 
btnSearch_Click(object sender, EventArgs 
e)
        
{
            
BindGrid(true);
            
gvItem.Visible = true;

        }

        protected void 
chkSelectAll_CheckedChanged(object sender, EventArgs 
e)
        
{
            CheckBox 
chk;
            
foreach (GridViewRow rowItem in 
gvItem.Rows)
            
{
                
chk = 
(CheckBox)(rowItem.Cells[0].FindControl("selected"));
                
chk.Checked = 
((CheckBox)sender).Checked;
            
}
        
}
        //Bind the GridView to with the 
Database returned records
        private 
void BindGrid(bool Reload)
        
{
            
DataTable dtItemRecords = 
null;
            if 
(Reload)
            
//get from database and bind to 
GV
            
{
                
dtItemRecords = 
osdb.Get_ItemRecords(tbSearchItemName.Text).Tables[0];
                
ViewState[viewStateGVName] = 
dtItemRecords;
            
}
            
else
            
{   

                
//retrive the view state object data table from previous 
retrival
                
dtItemRecords = ViewState[viewStateGVName] as 
DataTable;
            
}

            if 
(dtItemRecords != 
null)
            
{
                
gvItem.Columns[GVCHKBOX].Visible = 
true;
                
gvItem.DataSource = 
ViewState[viewStateGVName];
                
gvItem.AllowSorting = 
true;
                
gvItem.DataBind();


            
}
            
else
            
{
                
dtTemplateRecords.Rows.Add(dtItemRecordss.NewRow());

                
ViewState[viewStateGVName] = 
dtItemRecords;
                
gvItem.AllowSorting = 
false;
                
gvItem.DataSource = 
ViewState[viewStateGVName];
                
gvItem.DataBind();

                
//hide the checkbox and edit 
columns
                
gvItem.Columns[GVCHKBOX].Visible = 
false;
                
gvItem.Columns[GVEDITBTN].Visible = false;

                
int TotalColumns = 
dtItemRecords.Rows[0].Cells.Count;
                
gvItem.Rows[0].Cells.Clear();
                
gvItem.Rows[0].Cells.Add(new 
TableCell());
                
gvItem.Rows[0].Cells[0].ColumnSpan = 
TotalColumns;
                
gvItem.Rows[0].Cells[0].Text = "No Record 
Found";
            
}

           
}
    }
}

Sometimes the error will be GET_ItemRecords have no parameters but i have alrd passed in. Thanks. Hope to hear from u guys soon!