code: public List<FileCharacteristic> getCharacteristics() {
          long value = get(CHARACTERISTICS);
          List<FileCharacteristic> characteristics = FileCharacteristic
                  .getAllFor(value);
          // ensurance
          assert characteristics != null;
          return characteristics;
      }
docs: Returns a list with all characteristics of the file.
  <p>
  Ensures that the result is never null.
  
  @return list of file characteristics