guava/src/com/google/common/base/Optional.java
public java.util.Optional<T> toJavaUtil() {
    return java.util.Optional.ofNullable(orNull());
  }
public java.util.Optional<T> toJavaUtil() {
    return java.util.Optional.ofNullable(orNull());
  }
Returns the equivalent {@code java.util.Optional} value to this optional.

<p>Unfortunately, the method reference {@code Optional::toJavaUtil} will not work, because it
could refer to either the static or instance version of this method. Write out the lambda
expression {@code o -> o.toJavaUtil()} instead.

@since 21.0