Description of problem:
When accessing attributes "href_slug", "region_description", "region_number" and "image_href" of the "pictures" resource the request fails with internal server error:
{
    "error": {
        "kind": "internal_server_error",
        "message": "\"\\x89\" from ASCII-8BIT to UTF-8",
        "klass": "Encoding::UndefinedConversionError"
    }
}

All these attributes are listed by OPTIONS method.


Version-Release number of selected component (if applicable):
5.9.0.21
The identical requests work on 5.8.3.2


How reproducible:
100%


Steps to Reproduce:
1. create picture:
POST /api/pictures
{
	"action": "create",
	"content": "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mNk+M9QDwADhgGAWjR9awAAAABJRU5ErkJggg==",
	"extension": "png"
}
2. access attribute
GET /api/pictures/8?attributes=href_slug