Nested "required" fields pass validation when they are undefined and/or empty

[alexqfredrickson]

Observables within observable arrays which are "required" are passing validation even if they are undefined or empty.

To reproduce the issue, please see this JSFiddle. I have a form which collects information about dogs' names and breeds. The "Dog Breed" field is required. Also note that I have followed the examples here on how to validate nested values.

  function KnockoutViewModel() {
    var self = this;
    self.dogs = ko.observableArray([new Dog()]);
    self.submitForm = function() {
      console.log(self.dogs()[0].Breed());
    };
    
    self.validationObject = ko.validatedObservable({
        dogs: self.dogs
    });
  }

  function Dog() {
    var self = this;
    self.Name = ko.observable();
    self.Breed = ko.observable().extend({
      required: {
        params: true,
        message: "The dog's breed field is required."
      }
    });
    
    self.validationObject = ko.validatedObservable({
        Breed: self.Breed.extend({
            required: true
        })
    });
  }

To reproduce the issue:

1. Submit the form without a value in the "Dog Breed" field. validation successful
2. Enter a value into the "Dog Breed" field, delete it, and re-submit the form. validation successful
3. Enter a value into the "Dog Breed" field, submit the form, delete the value again, and resubmit the form. validation failed

I would expect (3) but not (1) and (2). Is this the intended behavior?

^{Note: I originally encountered this issue and described it in #636, but I'd initially missed the part of the documentation that states that special configuration is required to validate observables within observable arrays.}