code: @Override
      public MutableArray getArray(@NonNull String key) {
          return ((MutableDictionary) internalDict).getArray(key);
      }
docs: Get a property's value as a Array, which is a mapping object of an array value.
  Returns null if the property doesn't exists, or its value is not an array.
  
  @param key the key.
  @return the Array object.