Method: Returns true if no value is available, false otherwise.

Method: Returns true if a value is available, false otherwise.

Method: Returns this option if non-empty, or the passed option otherwise.

Method: This is similar to map() below except that the return value has no meaning; the passed callable is simply executed if the option is non-empty, and ignored if the option is empty.

Method: This is similar to map() except that the return value of the callable has no meaning.