Deserializing resource with relationships without includes fails

[dugsmith]

Here's the scenario. I have a resource that needs to be created with a relationships. I POST to the server /api/accountAuthorizations with this request body:

{
  "data": {
    "type": "accountAuthorization",
    "attributes": {
      "accountKey": "ACCT_ID1",
      "accessLevel": "full"
    },
    "relationships": {
      "saUser": {
        "data": {
          "id": "USER_ID1",
          "type": "saUser"
        }
      }
    }
  }
}

The response back from the server includes the data section of the relationships I passed in, like so:

{
    "data": {
        "id": "AUTH_ID1",
        "type": "accountAuthorization",
        "attributes": {
            "updatedBy": "USER_ID99",
            "accessLevel": "full",
            "createdBy": "USER_ID99",
            "accountKey": "ACCT_ID1"
        },
        "relationships": {
            "saUser": {
                "data": {
                    "id": "USER_ID1",
                    "type": "saUser"
                },
                "links": {
                    "self": "/api/accountAuthorizations/AUTH_ID1/relationships/saUser",
                    "related": "/api/accountAuthorizations/AUTH_ID1/saUser"
                }
            }
        },
        "links": {
            "self": "/api/accountAuthorizations/AUTH_ID1"
        }
    }
}

Unfortunately, json_api_client version 0.14.0 throws an exception when calling included_data_for on the resource while deserializing this response. Partial stack:

/ruby/2.4.0/lib/ruby/gems/2.4.0/gems/json_api_client-1.14.0/lib/json_api_client/included_data.rb:56:in `record_for'
/ruby/2.4.0/lib/ruby/gems/2.4.0/gems/json_api_client-1.14.0/lib/json_api_client/included_data.rb:44:in `data_for'
/ruby/2.4.0/lib/ruby/gems/2.4.0/gems/json_api_client-1.14.0/lib/json_api_client/resource.rb:534:in `included_data_for'

It appears that json_api_client expects that if the relationships has a resource with a data object like in my example, there must be a matching full resource in the included section of the response payload. This doesn't have that.

I don't see this requirement in the JSON:API spec, and the Java client I'm also testing with (Crnk) handles this gracefully.

I'm going to try and create a pull request that just returns a nil in included_data_for in this scenario.

[dugsmith]

FYI: this validator says the response above is valid: https://jsonapi-validator.herokuapp.com/.