title: Retrofit list of items always null
body: <p>I'm trying to get a list of items from a WS on my android app, but the response is always null.</p>
  
  <p>This is my code, and I can't figure it out:</p>
  
  <p>Interface:</p>
  
  <pre><code>public interface CategoriesInterface {
  
     @GET("/categories")
     List&lt;CategorieModel&gt; getCategories(@Query("k") String token);
  }
  </code></pre>
  
  <p>AsynkTask:</p>
  
  <pre><code>    new AsyncTask&lt;String, Void, Void&gt;() {
      @Override
      protected Void doInBackground(String... params) {
          try {
              Gson gson = new GsonBuilder().setDateFormat("yyyy-MM-dd HH:mm:ss").create();
  
              RestAdapter restAdapter = new RestAdapter.Builder()
                      .setEndpoint( "WS_URL" ) // The base API endpoint.
                      .setConverter( new GsonConverter(gson) )
                      .setLogLevel(RestAdapter.LogLevel.FULL)
                      .build();
  
              CategoriesInterface categoriesInterface = restAdapter.create( CategoriesInterface.class );
  
              List&lt;CategorieModel&gt; list = categoriesInterface.getCategories( params[0] );
  
              // LIST IS ALWAYS NULL
  
          } catch (RetrofitError error) {
              Log.e("ERROR", error.toString());
          }
  
          return null;
      }
  
  }.execute( token );
  </code></pre>
  
  <p>Model:</p>
  
  <pre><code>public class CategorieModel {
  
     @SerializedName("id")
     private String id;
  
     @SerializedName("cat_pt")
     private String cat_pt;
  
     @SerializedName("cat_es")
     private String cat_es;
  }
  </code></pre>
  
  <p>Response JSON format:</p>
  
  <pre><code> "categories": [
      {
          "id": "2",
          "cat_pt": “STRING",
          "cat_es": “STRING"
      },
  </code></pre>
  
  <p>I don't know what i'm doing wrong. The response List is always null.</p>
  
  <p>Thank you</p>