code: @Nonnull
      @SafeVarargs
      public static <T> NonEmptyImmutableList<T> of(@Nonnull T head, @Nonnull T... el) {
          if (el.length == 0) {
              return cons(head, ImmutableList.empty());
          }
          NonEmptyImmutableList<T> l = cons(el[el.length - 1], ImmutableList.empty());
          for (int i = el.length - 2; i >= 0; i--) {
              l = cons(el[i], l);
          }
          return cons(head, l);
      }
docs: A helper constructor to create a {@link NonEmptyImmutableList}.
  
  @param head The first element
  @param el   rest of the elements
  @param <T>  The type of the element
  @return a <code>NonEmptyImmutableList</code> of type <code>T</code>.