check if discriminator exist before calling it

Author: HugoMario

src/main/resources/handlebars/Java/libraries/okhttp-gson/JSON.mustache

@@ -61,6 +61,7 @@ public class JSON {
     public static GsonBuilder createGson() {
         GsonFireBuilder fireBuilder = new GsonFireBuilder()
         {{#parent}}
+        {{#discriminator}}
           .registerTypeSelector({{classname}}.class, new TypeSelector<{{classname}}>() {
             @Override
             public Class<? extends {{classname}}> getClassForElement(JsonElement readElement) {
@@ -108,6 +109,7 @@ public class JSON {
                   }
               }
           })
+        {{/discriminator}}
         {{/parent}}
         ;
         return fireBuilder.createGsonBuilder();