}
                    return null;
                }).filter(o -> o != null && keySet.add(o.getFirst())).collect(Collectors.toList()));
            }
            propMap.put(DEFAULT_SORT_VALUES, list);
        }
        return list.stream().map(p -> {
            final String key = p.getFirst();
            if (StringUtil.isEmpty(key) || userBean

     * @return the first element, or null if the collection is empty
     * @since Java 21
     */
    public static <E> E getFirst(final SequencedCollection<E> collection) {
        return collection.isEmpty() ? null : collection.getFirst();
    }

    /**
     * Returns the last element of a sequenced collection.
     *
     * @param <E> the element type

        }
    }

    @Override
    protected void writeHeaders(final HttpServletResponse response) {
        ComponentUtil.getFessConfig().getApiJsonResponseHeaderList().forEach(e -> response.setHeader(e.getFirst(), e.getSecond()));
    }

    /**
     * Writes a JSON response.
     * @param status The status code.
     * @param t The throwable.
     */

    }

    <T> void clearReferenceQueue(ReferenceQueue<T> referenceQueue) {
      while (referenceQueue.poll() != null) {}
    }

    /** Returns first entry of bin for given hash. */
    @Nullable E getFirst(int hash) {
      // read this volatile field only once
      AtomicReferenceArray<E> table = this.table;
      return table.get(hash & (table.length() - 1));
    }

                    logger.warn("DefaultHttpClient does not have {}.", propertyName);
                }
            }
        }

        formSchemeList.forEach(p -> {
            final FormScheme scheme = p.getFirst();
            final Credentials credentials = p.getSecond();
            scheme.authenticate(credentials, (request, consumer) -> {

                // request header

    }
  }

  /**
   * Returns the next element in {@code iterator} or {@code defaultValue} if the iterator is empty.
   * The {@link Iterables} analog to this method is {@link Iterables#getFirst}.
   *
   * @param defaultValue the default value to return if the iterator is empty
   * @return the next element of {@code iterator} or the default value
   * @since 7.0
   */
  @ParametricNullness