docs: public static <T> Collection<T> unique(Collection<T> self, boolean mutate, @ClosureParams(value=FromString.class, options={"T","T,T"}) Closure closure) {
          // use a comparator of one item or two
          int params = closure.getMaximumNumberOfParameters();
          if (params == 1) {
              self = unique(self, mutate, new OrderBy<T>(closure, true));
          } else {
              self = unique(self, mutate, new ClosureComparator<T>(closure));
          }
          return self;
      }