Get all objects where optional exists in Realm Swift
<p>If I have an optional var in my realm object, how would I get all instances an array of all instances where that var has not been set. For instance, get all instances of the <code>Person</code> who do not have an <code>Address</code>? Or all that <strong>do</strong> have an <code>Address</code>?</p>

<pre><code>class Person: Object {
    dynamic var address: Address?
    // more values
}
</code></pre>