code: @SuppressWarnings("unchecked")
      public static <Item> Item[] flatten(final Item... items) {
          return (Item[]) flattenAsStream(items).toArray(Object[]::new);
      }
docs: Returns an array of all Items specified as a comma separated list to the
  specified {@link List}, recursively collected from contained arrays.
  
  @param <Item>
  type of the specified items
  
  @param items
  comma separated liet of items
  
  @return array of all collected Items