title: Groovy/Grails autoconvert NaN string to double field
body: <p>I want to let users edit a field with double data in Grails view. I want to allow Double.NaN (to void values).</p>
  
  <p>There is a special char looking like a diamond with a question mark in it (in HTML) that acts like NaN, but - well - the users wont find that on their keys.</p>
  
  <p>In Java it works with <code>Double.valueOf("NaN")</code>. But typing NaN in the input field will throw a IllegalArgumentException saying "NaN" is an Unparseable Number.</p>
  
  <p>What method is callled for conversion? Whats the key to let it autoconvert to a double?</p>