code: private int getNextDataUsageIndex() throws PropertyException {
          Set<Integer> usedIndexes = getDataUsageNameIndexes();
          int nextIndex = 1;
          while (usedIndexes.contains(nextIndex)) {
              nextIndex++;
          }
          return nextIndex;
      }
docs: Returns the lowest unused index for data usage names.<br>
  Data usage names are enumerated (DATA_USAGE_1, DATA_USAGE_2, ...).<br>
  When new data usages are added, the lowest unused index is used as
  property name.
  
  @return The lowest free index to be used for data usage naming.
  @throws PropertyException if the extraction of used indexes fails.
  @see #getDataUsageNameIndexes()