title: Cannot call method indexOf undefined
body: <p>I'm getting the error, cannotcall method indexOf 'undefined' when using the ko utils array Filter . . .</p>
  
  <p>View Model:</p>
  
  <pre><code>viewModel.People = ko.mapping.fromJS(people);
  
  
  self.Filter1 = ko.observable();    
  
  
  
  self.FilteredSystem = ko.computed(function () {
  
      var Filter1 = self.Filter1();
  
  
          return ko.utils.arrayFilter(viewModel.People(), function (People) {
  
              return ((People.Name.indexOf(Filter1) !== -1));
  
          });
  
  
  }, self);
  </code></pre>