[Bug] Timeout error when including non-existing relationships

[Windvis]

When you include a relationship that doesn't exist the service hangs and times out after a minute with a 504 Gateway time-out error.

Example request: GET /resource-name?include=non-existing-relationship

According to the spec it should return a 400 Bad request response instead:

If a server is unable to identify a relationship path or does not support inclusion of resources from a path, it MUST respond with 400 Bad Request.