;boolean&nbsp;nillable</pre>
<div class="block">If true, the absence of the collection is represented by
 using <code>xsi:nil='true'</code>. Otherwise, it is represented by
 the absence of the element.</div>
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<dt>Default:</dt>
<dd>false</dd>
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<h4>required</h4>
<pre>public abstract&nbsp;boolean&nbsp;required</pre>
<div class="block">Customize th