code: public static <E> E one(E[] array) {
          return new OneElement<E>().apply(new ArrayIterator<>(array));
      }
docs: Yields the only element.
  
  @param <E> the element type parameter
  @param array the array to be searched
  @throws IllegalStateException if more than one element is found
  @throws IllegalArgumentException if no element matches
  @return the found element