code: protected static UnitFactorSet getDefaultFactorSet(UnitCategory category, UnitConverter converter) {
      switch (category) {
        case ANGLE:
          return UnitFactorSets.ANGLE;
        case AREA:
          return converter.areaFactors();
        case DURATION:
          return UnitFactorSets.DURATION;
        case ELECTRIC:
          return UnitFactorSets.ELECTRIC;
        case ENERGY:
          return converter.energyFactors();
        case FREQUENCY:
          return UnitFactorSets.FREQUENCY;
        case LENGTH:
          return converter.lengthFactors();
        case MASS:
          return converter.massFactors();
        case POWER:
          return UnitFactorSets.POWER;
        case VOLUME:
          return converter.volumeFactors();
        default:
          break;
      }
      return null;
    }
docs: Default conversion factors for each category. Some of these differ based on the locale
  of the converter.