Convert GsonBuilder into Kotlin

Does anyone know how to convert this code into kotlin

GsonBuilder builder = new GsonBuilder();
builder.setLenient();
builder.registerTypeAdapter(Date.class, new JsonDeserializer<Date>() {
        @Override
        public Date deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
            if (json.getAsJsonPrimitive().isNumber()) {
                return new Date(json.getAsJsonPrimitive().getAsLong() * 1000);
            } else {
                return null;
            }
        }
    });
return builder.create();

Then, i tried

val builder = GsonBuilder()
builder.setLenient()
builder.registerTypeAdapter(Date::class.java,.........)
return builder.create()

..... i can't figured it out how to convert the code