code: public final Mono<T> elementAt(int index, T defaultValue) {
  		return Mono.onAssembly(new MonoElementAt<>(this, index, defaultValue));
  	}
docs: Emit only the element at the given index position or fall back to a
  default value if the sequence is shorter.
  
  <p>
  <img class="marble" src="doc-files/marbles/elementAtWithDefault.svg" alt="">
  
  @reactor.discard This operator discards elements that appear before the requested index.
  
  @param index zero-based index of the only item to emit
  @param defaultValue a default value to emit if the sequence is shorter
  
  @return a {@link Mono} of the item at the specified zero-based index or a default value