Uncaught TypeError: Cannot read property 'defaultSelected' of undefined

[nevenduranec]

Steps to reproduce:

• go to: https://geminilabs.github.io/float-labels.js/
• use the browser back button
• use the browser forward button
• script errors out

float-labels.js@316

var selected = el.options[el.selectedIndex].defaultSelected !== true ? true : false;