code: public double optDouble(int index, double fallback) {
  		Object object = opt(index);
  		Double result = JSON.toDouble(object);
  		return result != null ? result : fallback;
  	}
docs: Returns the value at {@code index} if it exists and is a double or can be coerced
  to a double. Returns {@code fallback} otherwise.
  @param index the index to get the value from
  @param fallback the fallback value
  @return the value at {@code index} of {@code fallback}