Null relationships have a self link that results in an uncaught exception if retrieved

Using the example app as the starting point, I modeled a folder heirarchy using a "folders" resource that refers to another "folders" resource through a parent attribute. There is a case where a folders resource doesn't have a parent as it will be the root folder. The folders resource can be retrieved and shows the following relationship attribute for parent:

parent": {
    "meta": 
   {
      "relation": "primary",
      "readOnly": false
   },
   "links": 
    {
        "self": "http://localhost:8080/rest/folders/6b017640-827c-4d50-8dcc-79d766abb408/relationships/parent",
        "related": "http://localhost:8080/rest/folders/6b017640-827c-4d50-8dcc-79d766abb408/parent"
    },
    "data": null
}

The problem is if you follow the "related" link it will crash the server with the following exception...

/jsonapi-test/node_modules/jsonapi-server/lib/postProcess.js:41
    map[dataItem.type] = map[dataItem.type] || [ ];
                ^

TypeError: Cannot read property 'type' of null
    at /jsonapi-test/node_modules/jsonapi-server/lib/postProcess.js:41:17
    at Array.reduce (native)
    at Object.postProcess._fetchRelatedResources (/jsonapi-test/node_modules/jsonapi-server/lib/postProcess.js:40:36)
    at async.waterfall.relatedResources (/jsonapi-test/node_modules/jsonapi-server/lib/routes/related.js:51:21)
    at fn (/jsonapi-test/node_modules/async/lib/async.js:746:34)
    at /jsonapi-test/node_modules/async/lib/async.js:1213:16
    at /jsonapi-test/node_modules/async/lib/async.js:166:37
    at /jsonapi-test/node_modules/async/lib/async.js:706:43
    at /jsonapi-test/node_modules/async/lib/async.js:167:37
    at Immediate._onImmediate (/jsonapi-test/node_modules/async/lib/async.js:1206:34)

It seems to me a valid use case but in this case the links attribute would need to be removed but the issue would still remain that if somebody manually creates their own link it will bring down the server.

I've put up a test repository showing my set up at https://github.com/dalane/jsonapi-test

[pmcnr-hx]

Hi @dalane, thanks for reporting this and providing the test code. I've reproduced the issue and you are correct that the specification allows for data to be null in which case I believe the related link shouldn't be generated. I've had a look at the code and the fix should be fairly straightforward. I'll probably create a branch with the fix from which you will be able to install, but the project owner is currently on leave an we may have to wait a few days for a new release with the fixed issue.