title: knockout: ko observable without a default value
body: <p>I am just learning knockout, came across the tutorials to work with lists.</p>
  
  <pre><code>function SeatReservation(name, initialMeal) {
      var self = this;
      self.name = name;
      self.meal = ko.observable(initialMeal);
  
      self.formattedPrice = ko.computed(function() {
          var price = self.meal().price;
          return price ? "$" + price.toFixed(2) : "None";        
      });
  }
  </code></pre>
  
  <p>In the tutorial, this code defines an observable meal, that will be the choice selected in a dropdown select. In case if I do not have a default value, say for example I want to use a radio group instead of select. I want to be able to create an observable without any default value. I tried with an empty string as default value, then it works</p>
  
  <pre><code>self.meal = ko.observable("");
  </code></pre>
  
  <p>whereas if I try null as a default value, the select options does not even appear.</p>
  
  <pre><code>self.meal = ko.observable(null); // not working
  </code></pre>
  
  <p>what is the right way to create an observable without default value?</p>