title: How to display placeholders in AngularJS for undefined expression values?
body: <p>If I have an expression <code>{{ x }}</code> and x is <code>undefined</code> or <code>null</code>, then how can I display a placeholder for it? </p>
  
  <p>I provided one solution in my answer, but I would like to know what other ways there are.
  Maybe, also for placeholder for promises.</p>