rem: return value != undefined || value != null; 
add: return value != null; 
context:   compact: function() {    return this.select(function(value) {      return value != undefined || value != null;    });  },
meta: 1164	/local1/tlutelli/issta_data/temp/all_js/javascript/2007_temp/2007/1164/cb2408a82c9bc93bef177dc33a8981bc36800839/prototype.js/buggy/tools/prototype.js