code: protected final Stringifier registerNullStringifier(final String nullValue) {
  		Stringifier nullStringifier = new Stringifier() {
  			public String toString(Object object) {
  				return nullValue;
  			}
  		};
  		compositeStringifier.setNullStringifier(nullStringifier);
  		return nullStringifier;
  	}
docs: Register a stringifier for null values.