Optional conversion from Guava to Java

Guava Release 21 introduced the toJavaUtil and fromJavaUtil conversion methods to the Optional class.

javaUtilOptional = Optional.toJavaUtil(guavaOptional);
guavaOptional    = Optional.fromJavaUtil(javaUtilOptional);

Under the hood it seems to be implemented largely as the suggestion in Kayaman's answer:

public java.util.Optional<T> toJavaUtil() {
    return java.util.Optional.ofNullable(orNull());
}

...

public static <T> Optional<T> fromJavaUtil(@Nullable java.util.Optional<T> javaUtilOptional) {
    return (javaUtilOptional == null) ? null : fromNullable(javaUtilOptional.orElse(null));
}

How about Optional javaOpt = Optional.ofNullable(guavaOpt.orNull());?

Use guava transformation

maybeSomething
    .transform(java.util.Optional::of).or(java.util.Optional.empty());