title: Throw/catch error when a variable is undefined using underscore
body: <p>I'd like to know if there is any solution to throw an error when a variable is not defined inside my template?</p>
  
  <p>Example:</p>
  
  <pre><code>function hello() {
      var data = { foo: 'hello' };
  
      //data.bar is undefined, data.bar will be replaced by an empty string by underscore
      var render = _.template('&lt;p&gt;&lt;%= data.foo %&gt;&lt;%= data.bar %&gt;&lt;/p&gt;', {data: data}); 
  
      //Rendering okay? true|false
      //if (render...)
  
  }
  </code></pre>
  
  <p>I'd like to throw an error if the variable data.boo is not defined after the call of the _.template function. Do you have any idea if it's possible to do something like that? I checked the documentation and didn't find anything interesting unfortunately...</p>
  
  <p>Thanks</p>