rem: return '#<Hash:{' + this.map(function(pair) { return pair.map(Object.inspect).join(': '); }).join(', ') + '}>'; 
add: return this.select(function(value) { return value != undefined || value != null; }); 
context:     return '#<Hash:{' + this.map(function(pair) {      return pair.map(Object.inspect).join(': ');    }).join(', ') + '}>';
meta: 2801	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/2801/7e143d2df37946a5416f0f043869478087652eb6/prototype.js/clean/examples/testcases/prototype.js