>null</code>.</p>
<p>If the equality relation used by the set is not identity,
then the returned object may not be <em>identical</em> to <code>object</code>.
Some set implementations may not be able to implement this method.
If the <a href="dart-collection/SetMixin/contains.html">contains</a> method is computed,
rather than being based on an actual object instance,
then there may not be a specific object instance representing the
set element.</p>
    </section>
    
    <section class="summary source-code" 