private static @Nullable Long durationInNanos(long duration, @Nullable TimeUnit unit) {
    return (unit == null) ? null : unit.toNanos(duration);
  }
private static @Nullable Long durationInNanos(long duration, @Nullable TimeUnit unit) {
    return (unit == null) ? null : unit.toNanos(duration);
  }
private static @ Nullable Long durationInNanos ( long duration , @ Nullable TimeUnit unit ) { return ( unit == null ) ? null : unit . toNanos ( duration ) ; }
Converts an expiration duration/unit pair into a single Long for hashing and equality. Uses
nanos to match CacheBuilder implementation.
Converts an expiration duration / unit pair into a single Long for hashing and equality . Uses nanos to match CacheBuilder implementation .