guava/src/com/google/common/base/Optional.java
public static <T> java.util.@Nullable Optional<T> toJavaUtil(
      @Nullable Optional<T> googleOptional) {
    return googleOptional == null ? null : googleOptional.toJavaUtil();
  }
public static <T> java.util.@Nullable Optional<T> toJavaUtil(
      @Nullable Optional<T> googleOptional) {
    return googleOptional == null ? null : googleOptional.toJavaUtil();
  }
Returns the equivalent {@code java.util.Optional} value to the given {@code
com.google.common.base.Optional}, or {@code null} if the argument is null.

<p>If {@code googleOptional} is known to be non-null, use {@code googleOptional.toJavaUtil()}
instead.

<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 -> Optional.toJavaUtil(o)} instead.

@since 21.0