reduce: don't execute function for collections of size 1

src/main/java/fi/solita/utils/functional/FunctionalImpl.java

@@ -412,7 +412,7 @@ static final <T extends SemiGroup<T>> Option<T> reduce(Iterable<? extends T> xs)
     }
 
     static final <T> T reduce(Monoid<T> monoid, Iterable<? extends T> xs) {
-        return xs == null ? null : fold(monoid, cons(monoid.zero(), xs)).get();
+        return fold(monoid, xs).getOrElse(monoid.zero());
     }
 
     static final <T,Z> Z fold(Z zero, Apply<Map.Entry<? extends Z,? extends T>, Z> f, Iterable<? extends T> xs) {