Currently, using an input with a property mapped to a null value throws an error.

Running this code

const kokua = require('kokua');

const data = {
  foo: null,
};

kokua(data, kokua.mt('hal'));

results in this error being thrown:

/node_modules/kokua/lib/plugins/hal.js:148
          if (curr["h:ref"] || curr["h:link"]) {
                  ^

TypeError: Cannot read property 'h:ref' of null

According to the HAL specification, the root object of a HAL document is a Resource Object. Resource Objects consist of JSON that represents the state of a particular resource, and have two reserved properties: _links and _embedded. The _embedded property may contain one or more objects that are recursively interpreted as Resources; just like the root object, these resources contain JSON representing state and, optionally, nested _links and _embedded properties.

The HAL fixture in this repo contains two different embedded documents. There's one at the top level:

And one nested inside of a top-level sales property:

I can't find anything in the spec that describes or permits nesting of _embedded resources outside of the top level in the way that the fixture nests _embedded resources inside of sales. There's no precedent for it in the example document, and the Resource Object definition says that all non-reserved properties must be valid JSON representing the current state of the Resource.

Based on the HAL spec, it seems that only values mapped by a top-level _embedded property should be recursively interpreted as HAL documents, and that all other top-level fields (like sales, currentlyProcessing, and shippedToday) should be treated as JSON representing resource state, and not subjected to further HAL-specific semantics. This distinction has implications for the plugins that convert Hyper to HAL and back; specifically, processing the fixture in its current form requires recursive analysis of every property of the HAL document to check whether it contains any embedded documents, whereas the spec implies that the check only needs to be done when processing Resources (i.e. the root object or any objects mapped to by the _embedded property of a Resource).

Is there some other resource or specification that permits this kind of embedded document nesting, or does the fixture deviate from the spec?

Thanks!