code: public Multiset<T> set(final T e, final int occurrences) {
          checkOccurrences(occurrences);
  
          if (occurrences == 0) {
              valueMap.remove(e);
          } else {
              final MutableInt count = valueMap.get(e);
  
              if (count == null) {
                  valueMap.put(e, MutableInt.of(occurrences));
              } else {
                  count.setValue(occurrences);
              }
          }
  
          return this;
      }
docs: The element will be removed if the specified count is 0.
  
  @param e
  @param occurrences
  @return this Multiset.
  @throws IllegalArgumentException if the occurrences of element is less than 0