If a value is present, returns the value, otherwise throws {@code NoSuchElementException}.
If a value is present, performs the given action with the value, otherwise does nothing.
If a value is present, returns {@code true}, otherwise {@code false}.
Returns an empty {@code Nullable} instance. No value is present for this {@code Nullable}.
Returns an {@code Nullable} describing the given non-{@code null} value.
Returns an {@code Nullable} describing the given value, if non-{@code null}, otherwise returns an empty {@code Nullable}.