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