title: How to pass a key with null value or an empty String in the request body in retrofit android
body: <p>I need to pass the keys even with no values as the keys are mandatory at the server side. But Retrofit was removing the keys with null values while sending the request. How I can achieve sending keys without values to the server with the use of Retrofit?</p>
  
  <p>Request body look like this : </p>
  
  <pre><code>{
          "first_name":"testlogin",
          "last_name":"lastname",
          "username":"testman", 
          "password":"test123", 
          "email":"tester@test.com", 
          "address1":"123+test+way",
          **"address2":"",**
          **"address3":"",**
          "postal_code":"75023",
          "country":1,
          **"state":""**
  }
  </code></pre>
  
  <p>Thanks in advance.</p>