15.41. Nullness predicate

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Check a value for nullness.
Can be applied to basic attribute references, entity references and parameters.
HQL additionally allows it to be applied to component/embeddable types.

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<div class="title">Example 397. Nullness checking examples</div>
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<pre class="prettyprint highlight">`// select all persons with a nickname
List&lt;Person&gt; persons = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where p.nickName is not null", Person.class )
.getResultList();

// select all persons without a nickname
List&lt;Person&gt; persons = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where p.nickName is null", Person.class )
.getResultList();`</pre>
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