How to display empty number field in the gridpanel

[Mr.Techno]

Hi friends,
I am new to ext.net. i am exploring ext.net examples. I have one problem.
In my DataBase i have a table, in wchich a column has all integers and some NULL values. I get the data from this table and bind it to the gridpanel using store.

But in my gridpanel it is showing '0' instead of empty value. Please help me where i am doing wrong.

<ext:Store ID="testStore" runat="server" PruneModifiedRecords="true">
        <Reader>
            <ext:JsonReader>
                <Fields>
                    <ext:RecordField Name="VacationHours" Type="Int">
                    </ext:RecordField>
                    /*other fields here*/
                </Fields>
            </ext:JsonReader>
        </Reader>
    </ext:Store>

 <ext:GridPanel ID="GridPanel2" runat="server" StoreID="testStore" Height="600" Width="900"
                                Title="Test Grid">
                                <ColumnModel>
                                    <Columns>
                                        <ext:Column DataIndex="VacationHours" Header="VacationHours" Width="100">
                                        <Editor>
                                        <ext:NumberField ID="NumberField1" runat="server"
                                         EmptyText="testing Text" SelectOnFocus="true" MaxLength="4">
                                         
                                         </ext:NumberField>
                                            
                                        </Editor>
                                        </ext:Column>
                                       /*other columns*/
                                        <ext:CommandColumn Width="110">
                                            <Commands>
                                            
                                                <ext:GridCommand Icon="Delete" CommandName="CommandName" Text="Delete" Disabled="false" />
                                                
                                                <ext:GridCommand Icon="NoteEdit" CommandName="Edit" Text="Edit" />
                                                
                                            </Commands>
                                        </ext:CommandColumn>
                                        
                                    </Columns>
                                </ColumnModel>
                                <SelectionModel>
                                <ext:RowSelectionModel runat="server" ID="rowSelectionModel"></ext:RowSelectionModel>
                                </SelectionModel>
                                <Listeners> 
                                    <Command Handler="Ext.Msg.alert(command,record.data.Gender)" />
                                    
                                </Listeners>
                               
                            </ext:GridPanel>

Please see the below images i attached to know the original datatable and how it is appearing in the gridpanel.