title: Angular 2+ - check if Pipe returns an empty subset of original list
body: <p>I have a list of strings that I want to iterate through, but I want to be able to filter them using a search term. Like this:</p>
  
  <pre><code>&lt;div *ngFor="#item in list | search: searchTerm"&gt;{{ item }}&lt;/div&gt;
  </code></pre>
  
  <p><strong>My question is:</strong> how can I check if the pipe returns an empty subset of the list? </p>
  
  <p>In other words if none of the strings matches the search term, I want to display a message saying: "No matches".</p>