code: public static JsonArray getArray(JsonObject object, String field) {
          final JsonValue value = object.get(field);
          throwExceptionIfNull(value, field);
          return value.asArray();
      }
docs: Returns a field in a Json object as an array.
  Throws IllegalArgumentException if the field value is null.
  
  @param object the Json Object
  @param field the field in the Json object to return
  @return the Json field value as an array