title: How to negate a boolean expression when using the elvis operator in kotlin?
body: <p>I want to negate the following expression:</p>
  
  <p><code>return SpUtils.loadEMail()?.isEmpty() ?: false</code></p>
  
  <p>If i add a ! before the expression, like</p>
  
  <p><code>return !SpUtils.loadEMail()?.isEmpty() ?: false</code></p>
  
  <p>The IDE(Android Studio) tells me </p>
  
  <blockquote>
    <p>Only safe (?.) or non-null asserted (!!.) calls are allowed on a nullable receiver of type kotlin.Boolean?</p>
  </blockquote>
  
  <p>How do I negate this kinds of expressions?</p>