How can I disable input field spaces with MooTools?

How can I disable input field spaces with MooTools?

I can't find this anywhere, we need to disable the space bar (spaces) in a
input field of our form using MooTools 1.2
I have a solution for jQuery which doesn't work, however we have our site
based completely on our framework of choice.
Thank you for your help!!
<form action="signup.php" method="POST">
<input id='username' name='signup_username' type='text'
class='home_signin_field' maxlength='50' size='22'
onclick="this.value='';" onfocus="this.value='';"
onblur="this.value=!this.value?'Your Name':this.value;" value="Your Name">
</form>