title: How can I map an object in order to change it?
body: <p>I need to map an object </p>
  
  <pre><code>obj={a:'',b:firstname,c:'',d:lastname}
  </code></pre>
  
  <p>while mapping if an element of an object does contain : '', i will return to to <strong>null</strong> so the result will be like that : </p>
  
  <pre><code>obj={a:null,b:firstname,c:null,d:lastname}.
  </code></pre>
  
  <p>How can I do that?</p>