docs: @Nullable
      public String getFlashBiasDescription()
      {
          Integer value = _directory.getInteger(FocalLength.TAG_FLASH_BIAS);
  
          if (value == null)
              return null;
  
          boolean isNegative = false;
          if (value > 0xF000) {
              isNegative = true;
              value = 0xFFFF - value;
              value++;
          }
  
          // this tag is interesting in that the values returned are:
          //  0, 0.375, 0.5, 0.626, 1
          // not
          //  0, 0.33,  0.5, 0.66,  1
  
          return (isNegative ? "-" : "") + Float.toString(value / 32f) + " EV";
      }