title: java custom annotation: make an attribute optional
body: <p>I defined my own custom annotation</p>
  
  <pre><code>@Target(value={ElementType.METHOD, ElementType.FIELD})
  @Retention(RetentionPolicy.RUNTIME)
  public @interface MyCustomAnnotation  {
      Class&lt;?&gt; myType();
  }
  </code></pre>
  
  <p>how, if at all, can I make the attribute optional</p>