}
  }

  /**
   * A {@link Service} instance that does nothing. This is only useful as a placeholder to ensure
   * that the {@link ServiceManager} functions properly even when it is managing no services.
   *
   * <p>The use of this class is considered an implementation detail of ServiceManager and as such
   * it is excluded from {@link #servicesByState}, {@link #startupTimes}, {@link #toString} and all
   * logging statements.

 * implementations, except when the table is sparse.
 *
 * <p>Null row keys or column keys are not permitted.
 *
 * <p>This class provides methods involving the underlying array structure, where the array indices
 * correspond to the position of a row or column in the lists of allowed keys and values. See the

* <a href="https://github.com/tiangolo/full-stack" class="external-link" target="_blank">https://github.com/tiangolo/full-stack</a>
* <a href="https://github.com/tiangolo/full-stack-flask-couchbase" class="external-link" target="_blank">https://github.com/tiangolo/full-stack-flask-couchbase</a>
* <a href="https://github.com/tiangolo/full-stack-flask-couchdb" class="external-link" target="_blank">https://github.com/tiangolo/full-stack-flask-couchdb</a>

* <a href="https://github.com/tiangolo/full-stack" class="external-link" target="_blank">https://github.com/tiangolo/full-stack</a>
* <a href="https://github.com/tiangolo/full-stack-flask-couchbase" class="external-link" target="_blank">https://github.com/tiangolo/full-stack-flask-couchbase</a>
* <a href="https://github.com/tiangolo/full-stack-flask-couchdb" class="external-link" target="_blank">https://github.com/tiangolo/full-stack-flask-couchdb</a>

 *
 * <p>The following parameters are managed:</p>
 * <ul>
 *   <li>{@link UrlQueue} - The queue of URLs to be crawled.</li>
 *   <li>{@link CrawlerContext} - The context of the current crawling process.</li>
 *   <li>{@link UrlQueueService} - The service for managing the URL queue.</li>
 *   <li>{@link DataService} - The service for managing access results.</li>
 * </ul>
 *

    }

    /**
     * Returns a new instance of {@link DocumentBuilderFactory}.
     *
     * @return A new instance of {@link DocumentBuilderFactory}.
     */
    public static DocumentBuilderFactory newInstance() {
        return newInstance(false);
    }

    /**
     * Returns a new instance of {@link DocumentBuilderFactory}.
     *
     * @param external

 * by multiple threads.
 *
 * <p>Popular escapers are defined as constants in classes like {@link
 * com.google.common.html.HtmlEscapers} and {@link com.google.common.xml.XmlEscapers}. To create
 * your own escapers extend this class and implement the {@link #escape(int)} method.
 *
 * @author David Beaumont
 * @since 15.0
 */
@GwtCompatible

 * by multiple threads.
 *
 * <p>Popular escapers are defined as constants in classes like {@link
 * com.google.common.html.HtmlEscapers} and {@link com.google.common.xml.XmlEscapers}. To create
 * your own escapers extend this class and implement the {@link #escape(int)} method.
 *
 * @author David Beaumont
 * @since 15.0
 */
@GwtCompatible

   *
   * <ul>
   *   <li>{@code null} initial state, nothing has happened.
   *   <li>{@link Cancellation} terminal state, {@code cancel} was called.
   *   <li>{@link Failure} terminal state, {@code setException} was called.
   *   <li>{@link DelegatingToFuture} intermediate state, {@code setFuture} was called.
   *   <li>{@link #NULL} terminal state, {@code set(null)} was called.

    expectUnchanged();
  }

  private int aValidIndex() {
    return getList().size() / 2;
  }

  /**
   * Returns the {@link java.lang.reflect.Method} instance for {@link #testSet_null()} so that tests
   * of {@link java.util.Collections#checkedCollection(java.util.Collection, Class)} can suppress it
   * with {@code FeatureSpecificTestSuiteBuilder.suppressing()} until <a