Is there a preferred type for an Observable with no need for a value in Next events?
<p>I have an Observable which is only used for triggering <code>flatMap</code>/<code>map</code>.  So I only ever need the <code>Next</code> event and never a value.  I could use my own concept for such a trash value, but I'm wondering if there's an RxSwift convention for it.</p>

<p>Here's what I'm dealing with:</p>

<pre><code>// I'd rather not have an Element type that someone might use
let triggeringObservable: Observable&lt;SomeSessionClass&gt; 

// ...

triggeringObservable.map { _ -&gt; String in // The actual value is ignored
    return SomeLibrary.username() // `username()` is only ready when `triggeringObservable` sends Next
}
</code></pre>

<p>In this example, <code>triggeringObservable</code> is <code>rx_observer</code> on some property in the library which will let us know that <code>username()</code> is ready to be called.</p>