code: @NullSafe
    public static int sum(final int... numbers) {
      int sum = 0;
  
      if (numbers != null) {
        for (int number : numbers) {
          sum += number;
        }
      }
  
      return sum;
    }
docs: Calculates the sum of all integer values in the array.
  
  @param numbers an array of integer values to sum up.
  @return the sum of all integer values in the array.