public static Double unwrap(@SuppressWarnings("OptionalUsedAsFieldOrParameterType") OptionalDouble optional) {
        if (optional == null) {
            return null;
        } else {
            return optional.isPresent() ? optional.getAsDouble() : null;
        }
    }
Convert an optional value to a boxed one. If the inner value is
empty, {@code null} will be returned.

@param optional  the optional value (or null)
@return          the inner value or {@code null}
runtime-parent/runtime-core/src/main/java/com/speedment/runtime/core/util/OptionalUtil.java