"block">(Optional) Whether the association is optional. If set 
 to false then a non-null relationship must always exist.</div>
<dl>
<dt>Default:</dt>
<dd>true</dd>
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<h4>mappedBy</h4>
<pre>public abstract&nbsp;<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a>&nb