Using-the-Null-value

                              Runat="server"
                      DataSourceID="SqlDataSource1"
                      DataKeyNames="CustomerID"
                      AutoGenerateColumns="False"
                      AllowSorting="True"
                      AllowPaging="True"
                      PageSize="10">

                                         FirstPageText="Go to the first page"
                            LastPageText="Go to the last page"
                            Mode="NextPreviousFirstLast">


                                                HeaderText="CustomerID"
                                DataField="CustomerID"
                                SortExpression="CustomerID"/>
                                                DataField="CompanyName"
                                SortExpression="CompanyName"/>
                                                DataField="ContactName"
                                SortExpression="ContactName"/>
                                                DataField="ContactTitle"
                                SortExpression="ContactTitle"/>
                                                DataField="Address"
                                SortExpression="Address"/>
                                                DataField="City"
                                SortExpression="City"/>
                                                NullDisplayText="N/A"
                                DataField="Region"
                                SortExpression="Region"/>
                                                DataField="PostalCode"
                                SortExpression="PostalCode"/>
                                                DataField="Country"
                                SortExpression="Country"/>
                                                DataField="Phone"
                                SortExpression="Phone"/>
                                                DataField="Fax"
                                SortExpression="Fax"/>


                                   Runat="server"
                           SelectCommand="SELECT * FROM [Customers]"
                           ConnectionString="<%$ ConnectionStrings:AppConnectionString1 %>"
                           DataSourceMode="DataSet"
                           ConflictDetection="CompareAllValues" EnableCaching="True"
                           CacheKeyDependency="MyKey"
                           CacheDuration="Infinite">

Data Binding ASP.Net Tutorial