code: public boolean isNull(int index) {
  		Object value = opt(index);
  		return value == null || value == JSONObject.NULL;
  	}
docs: Returns true if this array has no value at {@code index}, or if its value is the
  {@code null} reference or {@link JSONObject#NULL}.
  @param index the index to set the value to
  @return true if this array has no value at {@code index}