[SalesForce] Navigation and PageReference in Lightning Component – Why is url void

UPDATE: I just verified it works when I navigate to my Lightning Component as part of a Lightning Page.

My company is still in classic, so we're wrapping our components in Visualforce. https://developer.salesforce.com/docs/atlas.en-us.lightning.meta/lightning/components_visualforce.htm

Now, the question is how do I make PageReference/Navigation Link work in a Component, within a Visualforce page?

I've also now tried force:navigateToURL. Works fine when the component is in a Lightning Page, errors in a VF page.
https://developer.salesforce.com/docs/component-library/bundle/force:navigateToURL/documentation

PRIOR:
DefaultUrl seems to work as expected, but url is returning void. Why is that? I've tried other PageReference types, and url is always void.

<aura:component access="public" implements="force:appHostable,lightning:isUrlAddressable">
<aura:attribute name="url" type="String" />
<aura:attribute name="pageReference" type="Object"/>

<aura:handler name="init" value="{! this }" action="{! c.init }"/>


<lightning:navigation aura:id="navService"/>
<a href="{!v.url}">Link</a>

({
init : function(component, event, helper) {
    var navService = component.find("navService");
    var pageReference = {
        type: 'standard__navItemPage',
        attributes: {
            apiName: "MyVisualForcePage"   
        }
    };
    component.set("v.pageReference", pageReference);
    // Set the URL on the link or use the default if there's an error
    var defaultUrl = "apex/MyVisualForcePage";
    navService.generateUrl(pageReference)
        .then($A.getCallback(function(url) {

            console.log('### url' + url);
            console.log('### defaultUrl' + defaultUrl);

            component.set("v.url", url ? url : defaultUrl);
        }), $A.getCallback(function(error) {
            component.set("v.url", defaultUrl);
        }));
}

})