title: Extjs store.proxy.extraParams is undefined only in Internet Explorer
body: <p>I have an ExtJs store.</p>
  
  <pre><code>var fieldsStore = new Ext.create('Ext.data.Store', {
  model : 'FieldsModel',
  proxy : {
      type : 'ajax',
      url : 'queryBuilder_getQueryDetails',
      extraParams : {
          queryID : queryID
      },
      reader : {
          type : 'json'
      }
  },
  listeners : {
      load : function(store, records, successful, operation, eOpts) {
          if (successful) {
              records.forEach(function(rec) {
                  // default settings: if datatype is INTEGER - SUM
                  if (rec.get('fieldType') == 'INTEGER') {
                      rec.set('fieldSettingKey', 'SUM');
                      rec.set('fieldSettingValue', 'Sum');
                  } else {
                      // else select ROWHEADER by default
                      rec.set('fieldSettingKey', 'ROWHEADER');
                      rec.set('fieldSettingValue', 'Row Header');
                  }
              });
              store.commitChanges();
          }
      }
  }
  });
  </code></pre>
  
  <p>Now when I do <code>fieldsStore.proxy.extraParams.queryID = arrQuery.queryId;</code>, I am getting an error in Internet Explorer. Not in Chrome or FF but only in IE.</p>
  
  <p>It says <code>fieldsStore.proxy.extraParams</code> is null or undefined. </p>
  
  <p>Can anyone help why this is happening only in IE?</p>