Add some comments

src/main/java/nouritsu/Dao.java

@@ -44,6 +44,7 @@ public class Dao {
     return "Cleared list of user “%s“".formatted(id);
   }
 
+  // The .exists() check is necessary because smembers throws an exception instead of returning null or an empty set.
   private Option<HashSet<String>> getSet(String key) {
     return withRedis(redis ->
       redis.exists(key)

src/main/java/nouritsu/Nouritsu.java

@@ -98,20 +98,20 @@ public class Nouritsu extends NanoHTTPD {
       .fold(Function.identity(), Resp.OK);
   }
 
+  // Return a Tuple2 containing the values of two eithers if both were Either.Right
+  private static <L, R1, R2> Either<L, Tuple2<R1, R2>> zip(Either<L, R1> first, Either<L, R2> second) {
+    return first.flatMap(f -> second.map(s -> Tuple.of(f, s)));
+  }
+
   private static String sortBySection(HashSet<ShoppingItem> items, Store store) {
     var itemsBySection = items.groupBy(ShoppingItem::section);
     var sorted = store.sections().flatMap(s -> itemsBySection.get(s).getOrElse(HashSet.empty()));
     var rest = items.removeAll(sorted);
-    var sortedString = sorted.map(ShoppingItem::name).mkString(", ");
+    var formattedItems = sorted.map(ShoppingItem::name).mkString(", ");
     if (rest.isEmpty()) {
-      return sortedString;
+      return formattedItems;
     }
-    return sortedString + rest.mkString("\nItems not available or not classified in this store: ", ", ", "");
+    return formattedItems + rest.mkString("\nItems not available or not classified in this store: ", ", ", "");
-  }
-
-  // Return a Tuple2 containing the values of two eithers if both were Either.Right
-  private static <L, R1, R2> Either<L, Tuple2<R1, R2>> zip(Either<L, R1> first, Either<L, R2> second) {
-    return first.flatMap(f -> second.map(s -> Tuple.of(f, s)));
   }
 
   private static Resp addToList(Map<String, String> params, Dao dao) {