code: public List<MediaType> getAccept() {
          if (isNull(accept)) {
              List<MediaType> accepts = getHeader(HeaderName.ACCEPT)
                  .map(MediaType::list)
                  .get();
  
              this.accept = nonEmpty(accepts) ? accepts : singletonList(WILDCARD);
          }
          return accept;
      }
docs: Returns a accept header value
  
  @return accept header value in {@link Optional} object