rem: if( !this.pageData[aPageTag] ) 
add: if( !(aPageTag in this.pageData) ) 
context:         getPageData:          function ( aPageTag )            {              if( !this.pageData[aPageTag] )                this.pageData[aPageTag] = [];              return this.pageData[aPageTag];            },
meta: 5872	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/5872/7d4ac1b07cd68f17f9d4cc23fab5b83496fc2271/nsWidgetStateManager.js/buggy/xpfe/global/resources/content/nsWidgetStateManager.js