docs: fix typo

java/lambdas/utilities-for-lists-and-maps/src/main/java/it/unibo/oop/lab/lambda/LambdaUtilities.java

@@ -105,7 +105,7 @@ public static <R, T> Map<R, Set<T>> group(final List<T> list, final Function<T,
      *            element type
      * @param <K>
      *            key type
-     * @return a map whose non present values are filled with the value provided
+     * @return a map whose non-present values are filled with the value provided
      *         by the supplier
      */
     public static <K, V> Map<K, V> fill(final Map<K, Optional<V>> map, final Supplier<V> def) {