Extjs null datefield

When there was two datefield existed in a form which one of them is notmandatory field, the allowBlank: true line or remove thecommand line of the field didn't solve the problem.

The form keep hanging when button save was clicked and the error messagecame as below:

[img_assist|nid=1006|title=errordate|desc=|link=none|align=left|width=640|height=131]

So, we have to control the field before submit to database.

Tarikh Mula: (mandatory field)

Tarikh Tamat: (not mandatory field)

/***Function***************************

//Insert new record

function createPrPerjawatan() {    

or 

//Update existing records

function savePrPerjawatan() { 

                var value =TarikhtamatField.getValue();

                        if(!Ext.isEmpty(value)){

                          value = value.format('Y-m-d');

                        } 

Ext.Ajax.request({

      url:'../phpcode/prperjawatan.php',

      params: {

         task: "UPDATE",                      

                          id_perjawatan:     id,

                          …

                         tarikh_mula:      TarikhmulaField.getValue().format('Y-m-d'),

                         tarikh_tamat:     value,

                         .... 

/****Form******************************

TarikhmulaField = new Ext.form.DateField({

                        id:'TarikhmulaField',

                        name:'tarikh_mula',

                        fieldLabel:'Tarikh Mula',

                        valueField:'tarikh_mula',

                        format :'d/m/Y',

                        allowBlank: false,

                        anchor:'65%',

                        blankText:'Ruangan ini perlu diisi!'

                        });           

            TarikhtamatField = newExt.form.DateField({

                        id:'TarikhtamatField',

                        name:'tarikh_tamat',

                        fieldLabel:'Tarikh Tamat',

                        valueField:'tarikh_tamat',

                        format :'d/m/Y',                       

                        anchor:'65%'

                        });                                

 That's all.