code: public LookupInBuilder exists(String path, SubdocOptionsBuilder optionsBuilder) {
          this.async.exists(path, optionsBuilder);
          return this;
      }
docs: Check if a value exists inside the document (if it does not, attempting to get the
  {@link DocumentFragment#content(int)} will raise an error).
  This doesn't transmit the value on the wire if it exists, saving the corresponding byte overhead.
  
  @param path the path inside the document to check for existence.
  @param optionsBuilder {@link SubdocOptionsBuilder}
  @return this builder for chaining.