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

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.}

Start with the linked JSFiddle reproduction and the repository's documentation on validating nested values. Trace how required validation is collected for observables inside observable arrays, then reproduce the three submission cases and add coverage for the expected failures in cases (1) and (2).