title: How to change default Nova Dropdown Dash (—)
body: <p>I have an BelongsTo Fields like this:</p>
  
  <pre><code>BelongsTo::make( __( 'Parent Page' ), 'parent', 'App\Nova\Page' )-&gt;nullable(),
  </code></pre>
  
  <p>In the Dropdown is as a Default Value a Dash (—) and I would like to change this label to something like "Main-Page".</p>
  
  <p>What I have now:
  <img src="https://i.stack.imgur.com/dEwum.png" alt="Situation Now"></p>
  
  <p>What I want to have
  <img src="https://i.stack.imgur.com/mjvnr.png" alt="What I Want"></p>