title: Binding NSSlider to NSTextField with nil minValue?
body: <p>I have an NSSlider bound to a text field to display the value given by the slider. 
  Everything works, but I would like the NSSlider to send "nil" as minValue to the object. </p>
  
  <p>For example, I can convert it to nil when saving (to a propertylist):</p>
  
  <pre><code>if ([myOb intValue] &gt; 0)
      [myDict setObject:... forKey:...]
  </code></pre>
  
  <p>But I would like to apply same behavior when the app is running, cause some other fields are enabled (with binding) only if the value of "myObj" is nil. The problem is the NSSlider always returns "0", and minValue=nil is not accepted by NSSlider. </p>
  
  <p>Thanks in advance, 
  Ronan.</p>