code: public static IdScopedByLocation from(@Nullable String locationId, String id) {
  
      checkNotNull(id);
      checkArgument(!id.isEmpty());
  
      if (locationId != null) {
        checkArgument(!locationId.isEmpty());
      }
  
      return new SlashEncodedIdScopedByLocation(locationId, id);
    }
docs: Creates a new scoped id using the supplied arguments.
  
  @param locationId the location part of the id (nullable).
  @param id the id part of the id (non null)
  @return a new scoped id.
  @throws NullPointerException if the supplied id is null.
  @throws IllegalArgumentException if the supplied strings are empty