return null;
        } catch (final Exception e) {
            throw new CrawlingAccessException("Failed to parse " + url, e);
        }
    }

    /**
     * Decodes a similar document hash from its compressed and encoded form.
     * Reverses the encoding process applied by encodeSimilarDocHash.
     *
     * @param hash the encoded hash string to decode

     * The path separator is {@code /} on all platforms, including Windows.
     * The prefix before the {@code :} character, if present and longer than 1 character, is the syntax.
     * If no syntax is specified, or if its length is 1 character (interpreted as a Windows drive),
     * the default is a Maven-specific variation of the {@code "glob"} pattern.
     *

 * It uses various services and components, such as {@link UrlQueueService}, {@link DataService},
 * {@link CrawlerContainer}, {@link LogHelper}, {@link CrawlerClientFactory}, and {@link CrawlerContext},
 * to perform its tasks.
 * </p>
 *
 * <p>
 * The crawling process involves the following steps:
 * </p>
 * <ol>
 *   <li>Fetching a URL from the queue using {@link UrlQueueService#poll(String)}.</li>

 * equals</i>. That is, {@code a.compareTo(b)} or {@code comparator.compare(a, b)} should equal zero
 * <i>if and only if</i> {@code a.equals(b)}. If this advice is not followed, the resulting map will
 * not correctly obey its specification.
 *
 * <p>See the Guava User Guide article on <a href=
 * "https://github.com/google/guava/wiki/ImmutableCollectionsExplained">immutable collections</a>.
 *
 * @author Jared Levy
 * @author Louis Wasserman

        return OptionalUtil.ofNullable(fileConfig);
    }

    /**
     * Gets all label types (collections) parsed from the GSA configuration.
     * Each label type represents a collection with its own URL filtering rules.
     *
     * @return an array of label types representing the parsed collections
     */
    public LabelType[] getLabelTypes() {
        return labelList.toArray(new LabelType[labelList.size()]);

 * <p>This class is not intended as a direct analogue of any existing "option" or "maybe" construct
 * from other programming environments, though it may bear some similarities.
 *
 * <p>An instance of this class is serializable if its reference is absent or is a serializable
 * object.
 *
 * <p><b>Comparison to {@code java.util.Optional} (JDK 8 and higher):</b> A new {@code Optional}

 *       (such as by passing an invalid argument), use the utilities of the {@link Preconditions}
 *       class instead.
 *   <li>If checking an <i>impossible</i> condition (which <i>cannot</i> happen unless your own
 *       class or its <i>trusted</i> dependencies is badly broken), this is what ordinary Java
 *       assertions are for. Note that assertions are not enabled by default; they are essentially
 *       considered "compiled comments."

/**
 * Base class for implementing services that can handle {@link #doStart} and {@link #doStop}
 * requests, responding to them with {@link #notifyStarted()} and {@link #notifyStopped()}
 * callbacks. Its subclasses must manage threads manually; consider {@link
 * AbstractExecutionThreadService} if you need only a single execution thread.
 *
 * @author Jesse Wilson
 * @author Luke Sandberg
 * @since 1.0
 */

  """Loop over user prompts for an ENV param until receiving a valid response.

  For the env param var_name, read from the environment or verify user input
  until receiving valid input. When done, set var_name in the environ_cp to its
  new value.

  Args:
    environ_cp: (Dict) copy of the os.environ.
    var_name: (String) string for name of environment variable, e.g. "TF_MYVAR".
    var_default: (String) default value string.

  private final Stats yStats;
  private final double sumOfProductsOfDeltas;

  /**
   * Internal constructor. Users should use {@link PairedStatsAccumulator#snapshot}.
   *
   * <p>To ensure that the created instance obeys its contract, the parameters should satisfy the
   * following constraints. This is the callers responsibility and is not enforced here.
   *
   * <ul>
   *   <li>Both {@code xStats} and {@code yStats} must have the same {@code count}.