rem: if( !this.pageData[aPageTag][aItemID] ) 
add: if( !(aItemID in this.pageData[aPageTag]) ) 
context:         getItemData:            function ( aPageTag, aItemID )            {              if( !this.pageData[aPageTag][aItemID] )                this.pageData[aPageTag][aItemID] = [];              return this.pageData[aPageTag][aItemID];            },
meta: 9421	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/9421/66c41c404dac77d053bf9bb78c8621d6e34494dc/nsWidgetStateManager.js/buggy/xpfe/global/resources/content/nsWidgetStateManager.js