public func optionally<X>(_ defineBlock: @escaping (SafeLink<B.WrappedType>) -> SafeLink<X>) -> SafeLink<B>

When B is an Optional you may call optionally. The supplied define block creates a subchain which will be run if the Optional value is non-nil. The SafeLink given to the define block yields a non-optional value of B.WrappedType to its child links This function returns a SafeLink with a void result value, because the subchain defined by optionally will not be executed if B is nil.