title: Gson serialization with dynamic field
body: <p>I faced a <strong>problem with json serialization with <code>Gson</code></strong>. So, I access an API using retrofit with dynamic returns as there's inconsistently json field.</p>
  
  <p><strong>The return looks like this:</strong></p>
  
  <pre><code>{
          "_id": "5959bace87b42b0012dd32e3",
          "user": {
              "_id": "58fdaca91ab5920012328669",
              "email": "xxx@xxxx.xx",
              "fullName": "User full name"
              "phonenumber": "+449xxxx",
              "profilePicture": ""
          }
       }
  </code></pre>
  
  <p><strong>But sometimes, the return would be like this (look at <code>user</code> field):</strong></p>
  
  <pre><code>{
              "_id": "5959bace87b42b0012dd32e3", 
              "user": "58fdaca91ab5920012328669"
  }
  </code></pre>
  
  <p><strong>This is my POJO</strong></p>
  
  <pre><code>public class Order{
  
     @PrimaryKey
     @SerializedName("_id")
     @Expose
     String id;
  
     @SerializedName("user")
     @Expose
     User user;
     //getter setter
  }
  </code></pre>
  
  <p>Anyone know how to solve this problem? </p>
  
  <p>Thanks</p>