AbstractSurrogateFragmentRenderer::containsNonScalars checks if URI attributes passed to ESI fragment renderer contain objects and if so, throws a deprecation notice. As I understand, arrays with scalar values should also be accepted, however, the method fails with arrays that contain pure scalar values.

It seems to me that the first if condition in the method should be:

if (is_array($value)) {
    return $this->containsNonScalars($value);
}

rather than:

if (is_array($value) && $this->containsNonScalars($value)) {
    return true;
}