code: public final int incMultiplicity(O object) throws ParameterException {
  		Validate.notNull(object);
  		if (!multiplicities.containsKey(object)) {
  			multiplicities.put(object, 1);
  			incMultiplicityCount(1);
  		} else {
  			Integer oldMultiplicity = multiplicities.get(object);
  			multiplicities.put(object, oldMultiplicity + 1);
  			decMultiplicityCount(oldMultiplicity);
  			incMultiplicityCount(oldMultiplicity + 1);
  		}
  		return multiplicity(object);
  	}
docs: Increments the multiplicity of the given object by 1.<br>
  In case the multiset does not contain the object, it is inserted with
  multiplicity 1.
  
  @param object The object for which the multiplicity should be
  incremented.
  @return
  @throws ParameterException