code: public int count(T obj, int count) {
          if (count < 1)
              throw new IllegalArgumentException("Count must be positive: " + count);
          int objIndex = (allowNewIndices) 
              ? objectIndices.index(obj)
              : objectIndices.find(obj);
          if (objIndex < 0)
              return 0;
          int curCount = indexToCount.get(objIndex);
          indexToCount.put(objIndex, curCount + count);
          sum += count;
          return curCount + count;
      }
docs: Counts the object, increasing its total count by the specified positive amount.
  
  @param count a positive value for the number of times the object occurred
  
  @throws IllegalArgumentException if {@code count} is not a positive value.