title: Return a completable in RxSwift without using a create block
body: <p>I have a Completable being returned from a simple function. 
  This is not an async call, so I just need to return a succcessful completion or error depending on a conditional (using Rx here so I can tie into other Rx usages):</p>
  
  <pre><code>func exampleFunc() -&gt; Completable {
      if successful {
          return Completable.just() // What to do here???
      } else {
          return Completable.error(SomeErrorType.someError)
      }
  }
  </code></pre>
  
  <p>The error case works pretty easily, but am having a block on how to just return a successful completable (without needing to <code>.create()</code> it). </p>
  
  <p>I was thinking I just need to use Completable's <code>.just()</code> or <code>.never()</code>, but <code>just</code> is requiring a parameter, and <code>never</code> doesn't seem to trigger the completion event.</p>