public RoutingContext setError(Error err) {
        node.setError(err);
        return this;
    }
<p>This is a convenience method to assign an {@link EmptyReply}
containing a single error to this. This also fiddles with the trace
object so that the error gets written to it.</p>

@param err The error to set.
@return This, to allow chaining.
@see #setReply(Reply)
messagebus/src/main/java/com/yahoo/messagebus/routing/RoutingContext.java