ExtJS XTemplate logic gave me to error as not deined

My store look like bellow

  var store_ = new Ext.data.JsonStore({
     mode: 'local',
     data: <?php echo $data ?>,
     fields: [
              'THUMBNAIL_SRC',
              'NAME',
              'REF_ID',
              'URL']
  });

I have another XTemplate code as bellow

var tpl = new Ext.XTemplate(
'<tpl for=".">',
'<div class="thumb-wrap" id="{NAME}">',
'<div class="thumb-inner"><div class="thumb-left">&nbsp;</div>',
'<div class="thumb">',
'<tpl if="(THUMBNAIL_SRC === \'\')">',
   '<img src="<?php echo BASE_DOMAIN ?>ddd" title="{NAME}">',
'<tpl else>',
   '<img src="<?php echo BASE_DOMAIN ?>aa{THUMBNAIL_SRC}" title="{NAME}">',
 '</tpl>',
'</div></div>',
'<span class="x-editable -landing">{NAME}</span></div>',
'</tpl>',
'<div class="x-clear"></div>'
);    

what i need in my XTemplate

WHEN store_.THUMBNAIL_SRC = '' THEN ddd image want to view ELSE THUMBNAIL_SRC image want to view END;

this is my basic logic for XTemplate but event time gave to me error as THUMBNAIL_SRC not defined i can't imagine what is the problem in my XTemplate please help