code: public void addUsedConverter(IConverter converter, Object sourceObject,
  			TypeReference<?> destinationType) {
  		UsedConverter usedConverter = new UsedConverter(converter,
  				sourceObject == null ? null : sourceObject.getClass(),
  				destinationType);
  		if (!usedConvertersSet.contains(usedConverter)) {
  			usedConvertersSet.add(usedConverter);
  			usedConvertersList.add(usedConverter);
  		}
  	}
docs: add a converter that has been used to convert from sourceObject to
  destination type (if it has not already been added)
  
  @param converter
  @param sourceObject
  @param destinationType