return (ImmutableSet<E>) RegularImmutableSet.EMPTY;
  }

  /**
   * Returns an immutable set containing the given element. Preferred over {@link
   * Collections#singleton} for code consistency, {@code null} rejection, and because the return
   * type conveys the immutability guarantee.
   */
  public static <E> ImmutableSet<E> of(E e1) {
    return new SingletonImmutableSet<>(e1);
  }

  /*

    }

    /**
     * Gets the XPath expression for selecting target nodes.
     *
     * @return the target node path
     */
    public String getTargetNodePath() {
        return targetNodePath;
    }

    /**
     * Sets the XPath expression for selecting target nodes.
     *
     * @param targetNodePath the target node path to set
     */

    /** The resource name for the MIME types configuration file. */
    protected static final String MIME_TYPES_RESOURCE_NAME = "/org/codelibs/fess/crawler/mime/tika-mimetypes.xml";

    /** The MimeTypes instance for detecting MIME types. */
    protected MimeTypes mimeTypes;

    /** Whether to use the filename for MIME type detection. */
    protected boolean useFilename = false;

    protected String lineSeparator = "\n";

    /** Separator for header-value association in text output. */
    protected String headerValueSeparator = ": ";

    /** Pattern for detecting quoted fields. */
    private static final Pattern QUOTED_FIELD_PATTERN = Pattern.compile("^\".*\"$");

    /**
     * Constructs a new CsvExtractor.
     */
    public CsvExtractor() {
        super();
    }

  protected Table<String, Integer, C> table;

  /**
   * Creates a table with the specified data.
   *
   * @param data the table data, repeating the sequence row key, column key, value once per mapping
   * @throws IllegalArgumentException if the size of {@code data} isn't a multiple of 3
   * @throws ClassCastException if a data element has the wrong type
   */

     *
     * Please note that the priority you assign to a page is not likely to
     * influence the position of your URLs in a search engine's result pages.
     * Search engines may use this information when selecting between URLs on
     * the same site, so you can use this tag to increase the likelihood that
     * your most important pages are present in a search index.
     *

  protected Table<String, Integer, C> table;

  /**
   * Creates a table with the specified data.
   *
   * @param data the table data, repeating the sequence row key, column key, value once per mapping
   * @throws IllegalArgumentException if the size of {@code data} isn't a multiple of 3
   * @throws ClassCastException if a data element has the wrong type
   */

    /** Pattern for detecting reserved characters in Lucene field queries. */
    public static final Pattern LUCENE_FIELD_RESERVED_PATTERN = Pattern.compile("([+\\-!\\(\\){}\\[\\]^\"~\\\\:\\p{Zs}]|(&&)|(\\|\\|))"); // "*", "?",

    /** Pattern for detecting reserved characters in Lucene range field queries. */

         * document.
         */
        private final Detector detector; // always set in the constructor

        /**
         * Creates an auto-detecting parser instance using the default Tika
         * configuration.
         */
        public TikaDetectParser() {
            this(tikaConfig);
        }

        /**
         * Constructor.

        } catch (final Exception e) {
            throw new CrawlerSystemException("Could not store data.", e);
        }
    }

    /**
     * Updates the character set of the response data by detecting it from the content.
     *
     * @param responseData the response data to update
     */
    protected void updateCharset(final ResponseData responseData) {