default ResourceReference refer() {
        return refer(null);
    }
<p>Creates a reference to this resource. You call this method to prevent an object from being
destroyed until you have finished using it.</p>

<p>You MUST keep the returned {@link ResourceReference} object and release the reference by calling
{@link ResourceReference#close()} on it. A reference created by this method can NOT be released by calling
{@link #release()}.</p>

@see ResourceReference#close()
jdisc_core/src/main/java/com/yahoo/jdisc/SharedResource.java