Including recursive relationships result in null object

[goranmoomin]

Including recursive relationships result in a null object.

A minimal example is here:
Backend
Frontend

As you see from the response of the API, jsonApi.findAll("a", { include: "b.a" }) should return an array with a objects that have an array with b objects which contain an a object. (Sorry for my poor English skills that can't explain it better than this.) However, the b objects' a field are always null, instead of the object.

For example, I would expect such output:

{
    "data": [
        {
            "id": "PpupN/bi1Eo8KtT/uHvm",
            "type": "as",
            "b": [],
            "links": {
                "self": "/as/PpupN%2Fbi1Eo8KtT%2FuHvm"
            }
        },
        {
            "id": "Ju6gn8yvL63rTN5Cr1zU",
            "type": "as",
            "b": [
                {
                    "id": "Z5ygOhd6cHqz1jU09maF",
                    "type": "bs",
                    "a":  {
                        "id": "Ju6gn8yvL63rTN5Cr1zU",
                        "type": "as",
                        "b": [],
                        "links": {
                            "self": "/as/Ju6gn8yvL63rTN5Cr1zU"
                        }
                    },
                    "links": {
                        "self": "/bs/Z5ygOhd6cHqz1jU09maF"
                    }
                }
            ],
            "links": {
                "self": "/as/Ju6gn8yvL63rTN5Cr1zU"
            }
        },
        {
            "id": "WFduHuyXYmkg6k6BCb+o",
            "type": "as",
            "b": [
                {
                    "id": "PoFSsKpm6ZaTkaaoj1Ln",
                    "type": "bs",
                    "a": {
                        "id": "WFduHuyXYmkg6k6BCb+o",
                        "type": "as",
                        "b": [],
                        "links": {
                            "self": "/as/WFduHuyXYmkg6k6BCb%2Bo"
                        }
                    },
                    "links": {
                        "self": "/bs/PoFSsKpm6ZaTkaaoj1Ln"
                    }
                },
                {
                    "id": "GLZwIT3E5p0dYzHD0l8z",
                    "type": "bs",
                    "a":  {
                        "id": "WFduHuyXYmkg6k6BCb+o",
                        "type": "as",
                        "b": [],
                        "links": {
                            "self": "/as/WFduHuyXYmkg6k6BCb%2Bo"
                        }
                    },
                    "links": {
                        "self": "/bs/GLZwIT3E5p0dYzHD0l8z"
                    }
                }
            ],
            "links": {
                "self": "/as/WFduHuyXYmkg6k6BCb%2Bo"
            }
        }
    ],
    "meta": {
        "count": 3
    },
    "links": {
        "self": "/as?include=b.a"
    }
}

However the current output is this:

{
    "data": [
        {
            "id": "PpupN/bi1Eo8KtT/uHvm",
            "type": "as",
            "b": [],
            "links": {
                "self": "/as/PpupN%2Fbi1Eo8KtT%2FuHvm"
            }
        },
        {
            "id": "Ju6gn8yvL63rTN5Cr1zU",
            "type": "as",
            "b": [
                {
                    "id": "Z5ygOhd6cHqz1jU09maF",
                    "type": "bs",
                    "a": null,
                    "links": {
                        "self": "/bs/Z5ygOhd6cHqz1jU09maF"
                    }
                }
            ],
            "links": {
                "self": "/as/Ju6gn8yvL63rTN5Cr1zU"
            }
        },
        {
            "id": "WFduHuyXYmkg6k6BCb+o",
            "type": "as",
            "b": [
                {
                    "id": "PoFSsKpm6ZaTkaaoj1Ln",
                    "type": "bs",
                    "a": null,
                    "links": {
                        "self": "/bs/PoFSsKpm6ZaTkaaoj1Ln"
                    }
                },
                {
                    "id": "GLZwIT3E5p0dYzHD0l8z",
                    "type": "bs",
                    "a": null,
                    "links": {
                        "self": "/bs/GLZwIT3E5p0dYzHD0l8z"
                    }
                }
            ],
            "links": {
                "self": "/as/WFduHuyXYmkg6k6BCb%2Bo"
            }
        }
    ],
    "meta": {
        "count": 3
    },
    "links": {
        "self": "/as?include=b.a"
    }
}