title: Why HttpParams doesn't work in multiple line in angular 4.3
body: <p>From Angular 4.3 they introduced HttpClient instead of Http. 
  in <code>HttpClient</code> I can't use <code>URLSearchParams</code> for url query parameter . instead of <code>URLSearchParams</code> I'm using <code>HttpParams</code></p>
  
  <p>This work</p>
  
  <pre><code> var params = new HttpParams().append('a', '1').append('b', '2');
  </code></pre>
  
  <p>But why this doesn't work</p>
  
  <pre><code>var params = new HttpParams();
  params.append('a', '1');
  params.append('b', '2');
  </code></pre>